Potomac River#South Branch Potomac River

File:Potomac River in District of Columbia IMG 4720.JPG, with Arlington Memorial Bridge in the foreground and Rosslyn, Arlington, Virginia in the background|right]]

The Potomac River runs {{cvt|405|mi}} from Fairfax Stone Historical Monument State Park in West Virginia on the Allegheny Plateau to Point Lookout, Maryland, and drains {{cvt|14679|sqmi|km2}}. The length of the river from the junction of its North and South Branches to Point Lookout is {{cvt|302|mi}}.

File:Physiographic provinces of the Mid-Atlantic region by NPS.png

The river has two sources. The source of the North Branch is at the Fairfax Stone located at the junction of Grant, Tucker, and Preston counties in West Virginia. The source of the South Branch is located near Hightown in northern Highland County, Virginia. The river's two branches converge just east of Green Spring in Hampshire County, West Virginia, to form the Potomac. As it flows from its headwaters down to the Chesapeake Bay, the Potomac traverses five geological provinces: the Appalachian Plateau, the Ridge and Valley, the Blue Ridge, the Piedmont Plateau, and the Atlantic coastal plain.

Once the Potomac drops from the Piedmont to the Coastal Plain at the Atlantic Seaboard fall line at Little Falls, tides further influence the river as it passes through Washington, D.C., and beyond. Salinity in the Potomac River Estuary increases thereafter with distance downstream. The estuary also widens, reaching 11 statute miles (17 km) wide at its mouth, between Point Lookout, Maryland, and Smith Point, Virginia, before flowing into the Chesapeake Bay.{{Potomac River routemap}}

{{Main|North Branch Potomac River}}

File:North Branch Potomac River Cumberland.jpg, and Ridgeley, West Virginia, in 2007]]

The source of the North Branch Potomac River is at the Fairfax Stone located at the junction of Grant, Tucker and Preston counties in West Virginia. From the Fairfax Stone, the North Branch Potomac River flows {{cvt|27|mi|km}} to the man-made Jennings Randolph Lake, an impoundment designed for flood control and emergency water supply. Below the dam, the North Branch cuts a serpentine path through the eastern Allegheny Mountains. First, it flows northeast by the communities of Bloomington, Luke, and Westernport in Maryland and then on by Keyser, West Virginia to Cumberland, Maryland. At Cumberland, the river turns southeast. {{convert|103|mi}} downstream from its source, the North Branch is joined by the South Branch between Green Spring and South Branch Depot, West Virginia from whence it flows past Hancock, Maryland and turns southeast once more on its way toward Washington, D.C., and the Chesapeake Bay.

{{Main|South Branch Potomac River}}

The South Branch's source is northwest of Hightown along U.S. Route 250 on the eastern side of Lantz Mountain (3,934 ft) in Highland County, Virginia. From Hightown, the South Branch is a small meandering stream that flows northeast along Blue Grass Valley Road through the communities of New Hampden and Blue Grass. At Forks of Waters, the South Branch joins with Strait Creek and flows north across the Virginia/West Virginia border into Pendleton County.

The river then travels on a northeastern course along the western side of Jack Mountain (4,045 ft), followed by Sandy Ridge (2,297 ft) along U.S. Route 220. North of the confluence of the South Branch with Smith Creek, the river flows along Town Mountain (2,848 ft) around Franklin at the junction of U.S. Route 220 and U.S. Route 33. After Franklin, the South Branch continues north through the Monongahela National Forest to Upper Tract where it joins with three sizeable streams: Reeds Creek, Mill Run, and Deer Run.

Between Big Mountain (2,582 ft) and Cave Mountain (2,821 ft), the South Branch bends around the Eagle Rock (1,483 ft) outcrop and continues its flow northward into Grant County. Into Grant, the South Branch follows the western side of Cave Mountain through the {{convert|20|mi|km|adj=on}} long Smoke Hole Canyon, until its confluence with the North Fork at Cabins, where it flows east to Petersburg. At Petersburg, the South Branch Valley Railroad begins, which parallels the river until its mouth at Green Spring.

File:Hanging Rocks Wappocomo WV 1890s.jpg on the South Branch in the 1890s]]

In its eastern course from Petersburg into Hardy County, the South Branch becomes more navigable allowing for canoes and smaller river vessels. The river splits and forms a series of large islands while it heads northeast to Moorefield. At Moorefield, the South Branch is joined by the South Fork South Branch Potomac River and runs north to Old Fields where it is fed by Anderson Run and Stony Run.

At McNeill, the South Branch flows into the Trough where it is bound to its west by Mill Creek Mountain (2,119 ft) and to its east by Sawmill Ridge (1,644 ft). This area is the habitat to bald eagles. The Trough passes into Hampshire County and ends at its confluence with Sawmill Run south of Glebe and Sector.

The South Branch continues north parallel to South Branch River Road (County Route 8) toward Romney with a number of historic plantation farms adjoining it. En route to Romney, the river is fed by Buffalo Run, Mill Run, McDowell Run, and Mill Creek at Vanderlip. The South Branch is traversed by the Northwestern Turnpike (U.S. Route 50) and joined by Sulphur Spring Run where it forms Valley View Island to the west of town.

Flowing north of Romney, the river still follows the eastern side of Mill Creek Mountain until it creates a horseshoe bend at Wappocomo's Hanging Rocks around the George W. Washington plantation, Ridgedale. To the west of Three Churches on the western side of South Branch Mountain, {{convert|3,028|ft|m}}, the South Branch creates a series of bends and flows to the northeast by Springfield through Blue's Ford. After two additional horseshoe bends (meanders), the South Branch flows under the old Baltimore and Ohio Railroad mainline between Green Spring and South Branch Depot, and joins the North Branch to form the Potomac.

This stretch encompasses the section of the Potomac River from the confluence of its North and South Branches through Opequon Creek near Shepherdstown, West Virginia.{{cite web |url=https://www.potomacriverkeepernetwork.org/ |title=Potomac Riverkeeper Network |date=2019 |website=www.potomacriverkeepernetwork.org |publisher=Potomac Riverkeeper Network |access-date=25 March 2019 |archive-date=November 19, 2020 |archive-url=https://web.archive.org/web/20201119163153/https://www.potomacriverkeepernetwork.org/ |url-status=live}} Along the way the following tributaries drain into the Potomac: North Branch Potomac River, South Branch Potomac River, Town Creek, Little Cacapon River, Sideling Hill Creek, Cacapon River, Sir Johns Run, Warm Spring Run, Tonoloway Creek, Fifteenmile Creek, Sleepy Creek, Cherry Run, Back Creek, Conococheague Creek, and Opequon Creek.

File:Aerial Photo of Harpers Ferry (15646790473).jpg

This section covers the Potomac from just above Harpers Ferry in West Virginia down to Little Falls, Maryland on the border between Maryland and Washington, DC. Along the way the following tributaries drain into the Potomac: Antietam Creek, Shenandoah River, Catoctin Creek (Virginia), Catoctin Creek (Maryland), Tuscarora Creek, Monocacy River, Little Monocacy River, Broad Run, Goose Creek, Broad Run, Horsepen Branch, Little Seneca Creek, Tenmile Creek, Great Seneca Creek, Old Sugarland Run, Muddy Branch, Nichols Run, Watts Branch, Limekiln Branch, Carroll Branch, Pond Run, Clarks Branch, Mine Run Branch, Difficult Run, Bullneck Run, Rock Run, Scott Run, Dead Run, Turkey Run, Cabin John Creek, Minnehaha Branch, and Little Falls Branch.

File:2016-08-28 10 15 51 View southwest across the Potomac River from the south end of Cobb Island Road on Cobb Island, Charles County, Maryland.jpg on Cobb Island, Charles County, Maryland ]]

The Tidal Potomac River lies below the Fall Line. This 108-mile (174-km) stretch encompasses the Potomac from a short distance below the Washington, DC - Montgomery County line, just downstream of the Little Falls of the Potomac River, to the Chesapeake Bay.{{cite web |title=Potomac River Basin Fact Sheet |url=https://www.potomacriver.org/wp-content/uploads/2014/11/Potomac-Basin-Fact-Sheet_Oct_2015.pdf |date=October 2015 |website=www.potomacriver.org |publisher=Interstate Commission on the Potomac River Basin (ICPRB) |access-date=28 March 2019 |archive-date=December 16, 2017 |archive-url=https://web.archive.org/web/20171216060733/http://www.potomacriver.org/wp-content/uploads/2014/11/Potomac-Basin-Fact-Sheet_Oct_2015.pdf |url-status=live}}

Along the way the following tributaries drain into the Potomac: Pimmit Run, Gulf Branch, Donaldson Run, Windy Run, Spout Run, Maddox Branch, Foundry Branch, Rock Creek, Rocky Run, Tiber Creek, Roaches Run, Washington Channel, Anacostia River, Four Mile Run, Oxon Creek, Hunting Creek, Broad Creek, Henson Creek, Swan Creek, Piscataway Creek, Little Hunting Creek, Dogue Creek, Accotink Creek, Pohick Creek, Pomonkey Creek, Occoquan River, Neabsco Creek, Powell's Creek, Mattawoman Creek, Chicamuxen Creek, Quantico Creek, Little Creek, Chopawamsic Creek, Tank Creek, Aquia Creek, Potomac Creek, Nanjemoy Creek, Chotank Creek, Port Tobacco River, Popes Creek, Gambo Creek, Clifton Creek, Piccowaxen Creek, Upper Machodoc Creek, Wicomico River, Cobb Island, Monroe Creek, Mattox Creek, Popes Creek, Breton Bay, Leonardtown, St. Marys River, Yeocomico River, Coan River, and Hull Creek.

The river itself is at least 3.5 million years old, likely extending back ten to twenty million years before the present when the Atlantic Ocean lowered and exposed coastal sediments along the fall line. This included the area at Great Falls, which eroded into its present form during recent glaciation periods.{{cite web |title=The River and the Rocks: The Geologic Story of Great Falls and the Potomac River Gorge |last=Reed |first=John Calvin |url=https://pubs.usgs.gov/bul/1471/report.pdf |website=pubs.usgs.gov |publisher=USGS |access-date=24 March 2019 |archive-date=October 1, 2020 |archive-url=https://web.archive.org/web/20201001233035/https://pubs.usgs.gov/bul/1471/report.pdf |url-status=live}}

The stream gradient of the entire river is 0.14%, a drop of 930 m over 652 km.

File:Detail of 1608 Smith Map showing the Patawomeck River.jpg

"Potomac" is a European spelling of Patawomeck, the Algonquian name of a Native American village on its southern bank.{{cite book |last=Bright |first=William |author-link=William Bright |title=Native American Placenames of the United States |url=https://books.google.com/books?id=5XfxzCm1qa4C&pg=PA396 |year=2004 |publisher=University of Oklahoma Press |isbn=978-0-8061-3598-4 |page=396 |url-status=live |archive-url=https://web.archive.org/web/20160511135133/https://books.google.com/books?id=5XfxzCm1qa4C&pg=PA396 |archive-date=May 11, 2016}} Native Americans had different names for different parts of the river, calling the river above Great Falls Cohongarooton, meaning "honking geese"Legends of Loudoun: An account of the history and homes of a border county of Virginia's Northern Neck, Harrison Williams, p. 26.{{cite book |last=Achenbach |first=Joel |title=The Grand Idea: George Washington's Potomac and the Race to the West |url=https://archive.org/details/grandideageorgew00ache |url-access=registration |year=2004 |publisher=Simon and Schuster |isbn=978-0-684-84857-0 |pages=[https://archive.org/details/grandideageorgew00ache/page/35 35]–36}} and "Patawomke" below the Falls, meaning "river of swans".Hagemann, James A. (1988). The Heritage of Virginia. The Donning Company, 2nd edition, 297 p. {{ISBN|0-89865-255-3}}. In 1608, Captain John Smith explored the river now known as the Potomac and made drawings of his observations which were later compiled into a map and published in London in 1612. This detail from that map shows his rendition of the river that the local tribes had told him was called the "Patawomeck". The spelling of the name has taken many forms over the years from "Patawomeck" (as on Captain John Smith's map) to "Patomake", "Patowmack", and numerous other variations in the 18th century and now "Potomac". The river's name was officially decided upon as "Potomac" by the Board on Geographic Names in 1931.{{Cite GNIS| 597915 |Potomac River}}

File:Tundra swans (6565983429).jpgs were the predominant species of swan on the Potomac River when the Algonquian tribes dwelled along its shores, and continue to be the most populous variety today.{{cite web |url=http://cbmm.org/news/chesapeake-swan-song-exhibition-opens-april-11-at-cbmm/ |title=Chesapeake Swan Song exhibition opens April 11 at CBMM |date=January 26, 2015 |publisher=Chesapeake Bay Maritime Museum |archive-url=https://archive.today/20180228140642/http://cbmm.org/news/chesapeake-swan-song-exhibition-opens-april-11-at-cbmm/ |archive-date=February 28, 2018 |url-status=live |access-date=February 28, 2018 |df=mdy-all}}]] The similarity of the name to the Ancient Greek word for river, potamos, has been noted for more than two centuries but it appears to be due to chance.{{cite book |last=Jefferson |first=Thomas |author-link=Thomas Jefferson |title=The Proceedings of the Government of the United States, in Maintaining the Public Right to the Beach of the Missisipi: Adjacent to New-Orleans, Against the Intrusion of Edward Livingston |url=https://books.google.com/books?id=Mpc0AQAAMAAJ&pg=PA200 |year=1814 |publisher=Edward J. Coale |pages=200– |quote=I have heard of an etymologist who derived the name of the river Potomac from the Greek Potamos. This derivation is quite as probable as that of beach from beotian; being founded on a much greater similarity of sound, as well as analogy of sense. |access-date=November 15, 2020 |archive-date=December 8, 2020 |archive-url=https://web.archive.org/web/20201208012813/https://books.google.com/books?id=Mpc0AQAAMAAJ&pg=PA200 |url-status=live}}{{cite book |last1=Campbell |first1=Douglas E. |last2=Sherman |first2=Thomas B. |title=On the Potomac River |url=https://books.google.com/books?id=Z4URBwAAQBAJ&pg=PA3 |date=25 July 2014 |isbn=978-1-304-69872-8 |pages=3– |publisher=Lulu.com |access-date=November 15, 2020 |archive-date=December 7, 2020 |archive-url=https://web.archive.org/web/20201207194351/https://books.google.com/books?id=Z4URBwAAQBAJ&pg=PA3 |url-status=live}}{{cite book |last1=Sorenson |first1=John L. |last2=Raish |first2=Martin |title=Pre-Columbian Contact with the Americas Across the Oceans: An Annotated Bibliography |url=https://books.google.com/books?id=6o_fAAAAMAAJ |year=1996 |publisher=Research Press |isbn=978-0-934893-23-7 |page=146 |access-date=November 15, 2020 |archive-date=December 8, 2020 |archive-url=https://web.archive.org/web/20201208012837/https://books.google.com/books?id=6o_fAAAAMAAJ |url-status=live}}

The Potomac River brings together a variety of cultures throughout the watershed from the coal miners of upstream West Virginia to the urban residents of the nation's capital and, along the lower Potomac, the watermen of Virginia's Northern Neck.

File:View of the Potomac River - George Washington Birthplace National Monument - Stierch - B.jpg in Westmoreland County, Virginia ]]

File:Potomac River Tourist Boat near Lincoln Memorial, Washington DC.jpg and under the Arlington Memorial Bridge]]

{{multiple image

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| header = Civil War Era

| image1 = Conferderate army crossing the Potomac River during the invasion of Maryland.jpg

| image2 = Defense of Washington - 6 views- 2 views of Chain Bridge, Pimmitt Run Bridge (small bridge near Chain Bridge), Block House for defense of Aqueduct Bridge, and Georgetown Ferry LCCN2003670507.jpg

| image3 = PR Chain Bridge Lower Battery ca 1862 LOC.jpg

| caption1 = Confederate troops crossing the fords of the Potomac in early September 1862 for the invasion of Maryland, which would culminate in the Battle of Antietam. (Print of a wood carving based on a drawing by Thomas Nast; first published in the September 27, 1862, edition of Harper's Weekly.)

| caption2 = Union defenses along the Potomac near Washington, DC
Top row: Chain Bridge (two views) and Pimmit Run Bridge; Bottom Row: Aqueduct Bridget {two views) and Georgetown Ferry

| caption3 = Union soldiers manning the Lower Battery at the north end of Chain Bridge in 1862

| image4 = Georgetown 1861.jpg

| caption4 = Union soldiers on the Potomac River across from Georgetown University in 1861

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Being situated in an area rich in American history and American heritage has led to the Potomac being nicknamed "the Nation's River". George Washington, the first President of the United States, was born in, surveyed, and spent most of his life within, the Potomac basin. All of Washington, D.C., the nation's capital city, also lies within the watershed. The First United States Congress by act of July 16, 1790 stated that the nation's capital was to be located on the river.Bugbee, Mary F. "The Early Planning of Sites for Federal and Local Use in Washington, D. C." Records of the Columbia Historical Society, Washington, D.C., vol. 51/52, 1951, p. 19. JSTOR, http://www.jstor.org/stable/40067294. Retrieved 19 Feb. 2024. The 1859 siege of Harper's Ferry at the river's confluence with the Shenandoah was a precursor to numerous epic battles of the American Civil War in and around the Potomac and its tributaries, such as the 1861 Battle of Ball's Bluff and the 1862 Battle of Shepherdstown.File:Map of the Potomac River ~1862 by Sneden LOC.jpg]]General Robert E. Lee crossed the river, thereby invading the North and threatening Washington, D.C., twice in campaigns climaxing in the battles of Antietam (September 17, 1862) and Gettysburg (July 1–3, 1863). Confederate General Jubal Early crossed the river in July 1864 on his attempted raid on the nation's capital. The river not only divided the Union from the Confederacy, but also gave name to the Union's largest army, the Army of the Potomac.{{cite book |last=Peck |first=Garrett |title=The Potomac River: A History and Guide |year=2012 |publisher=The History Press |location=Charleston, SC |isbn=978-1-60949-600-5 |page=18}}

The Patowmack Canal was intended by George Washington to connect the Tidewater region near Georgetown with Cumberland, Maryland. Started in 1785 on the Virginia side of the river, it was not completed until 1802. Financial troubles led to the closure of the canal in 1830. The Chesapeake and Ohio Canal operated along the banks of the Potomac in Maryland from 1831 to 1924 and also connected Cumberland to Washington, D.C.{{cite book |title=The Chesapeake & Ohio Canal: Pathway to the Nation's Capital |last=Hahn |first=Thomas |year=1984 |publisher=Scarecrow Press |location=Metuchen, NJ |isbn=0-8108-1732-2}} This allowed freight to be transported around the rapids known as the Great Falls of the Potomac River, as well as many other, smaller rapids.{{See also|Attempts to make the Potomac River navigable}}

File:Coast Guard, multiple partner agencies, responding to plane crash in Potomac River (8847923).jpg in the Potomac River, Washington, D.C.]]

Washington, D.C. began using the Potomac as its principal source of drinking water with the opening of the Washington Aqueduct in 1864, using a water intake constructed at Great Falls.Ways, Harry C. (1996). The Washington Aqueduct: 1852-1992. (Baltimore, MD: U.S. Army Corps of Engineers, Baltimore District)Washington Aqueduct

An average of approximately {{convert|486|e6USgal|m3}} of water is withdrawn daily from the Potomac in the Washington area for water supply, providing about 78 percent of the region's total water usage, this amount includes approximately 80 percent of the drinking water consumed by the region's estimated 6.1 million residents.{{cite web |url=https://www.census.gov/content/dam/Census/newsroom/releases/2016/cb16-cn43_table_6.pdf |title=The 10 Most Populous Metro Areas : July 1, 2015 |date=July 2015 |website=www.census.gov |publisher=US Census Bureau |access-date=April 9, 2019 |archive-date=November 4, 2020 |archive-url=https://web.archive.org/web/20201104162440/https://www.census.gov/content/dam/Census/newsroom/releases/2016/cb16-cn43_table_6.pdf |url-status=live}}

File:The Potomac River surges over Chain Bridge during 1936 Flood 19 March 1936.jpg during the historic 1936 flood. The bridge was so severely damaged by the raging water, and the debris it carried, that its superstructure had to be re-built; the new bridge was opened to traffic in 1939. (This photograph was taken from a vantage point on Glebe Road in Arlington County, Virginia. The houses on the bluffs in the background are located on the Potomac Palisades of Washington, DC.)]]

As a result of damaging floods in 1936 and 1937, the Army Corps of Engineers proposed the Potomac River basin reservoir projects, a series of dams that were intended to regulate the river and to provide a more reliable water supply. One dam was to be built at Little Falls, just north of Washington, backing its pool up to Great Falls. Just above Great Falls, the much larger Seneca Dam was proposed whose reservoir would extend to Harpers Ferry.{{cite news |url=https://news.google.com/newspapers?nid=1298&dat=19631204&id=cuQPAAAAIBAJ&pg=5587,5390295 |title=Potomac Dam Is Opposed By Virginians |last=Carey |first=Frank |date=December 4, 1963 |publisher=Fredericksburg Free-Lance Star |access-date=2009-11-13}} Several other dams were proposed for the Potomac and its tributaries.

When detailed studies were issued by the Corps in the 1950s, they met sustained opposition, led by U.S. Supreme Court Justice William O. Douglas, resulting in the plans' abandonment.{{cite news |url=https://www.washingtonpost.com/ac2/wp-dyn?pagename=article&node=&contentId=A13425-2002May1 |archive-url=https://web.archive.org/web/20020916051041/http://www.washingtonpost.com/ac2/wp-dyn?contentId=A13425-2002May1&node=&pagename=article |url-status=dead |archive-date=September 16, 2002 |title=America's River |author=Joel Achenbach |newspaper=The Washington Post |date=May 5, 2002 |pages=W12}} The only dam project that did get built was Jennings Randolph Lake on the North Branch.{{cite web |url=https://www.nab.usace.army.mil/portals/63/docs/factsheets/fy15_factsheets/md-wv-jenningsrandolphlake-om.pdf |title=Jennings Randolph Lake, MD & WV |date=February 2015 |website=www.nab.usace.army.mil |publisher=USACE (United States Corps of Engineers) |access-date=April 5, 2019 |archive-date=September 28, 2020 |archive-url=https://web.archive.org/web/20200928184024/https://www.nab.usace.army.mil/portals/63/docs/factsheets/fy15_factsheets/md-wv-jenningsrandolphlake-om.pdf |url-status=live}}

The Corps built a supplementary water intake for the Washington Aqueduct at Little Falls in 1959.Scott, Pamela (2007), [http://140.194.76.129/publications/eng-pamphlets/ep870-1-67/toc.htm "Capital Engineers: The U.S. Army Corps of Engineers in the Development of Washington, D.C., 1790–2004."] {{webarchive|url=https://web.archive.org/web/20120226045246/http://140.194.76.129/publications/eng-pamphlets/ep870-1-67/toc.htm |date=February 26, 2012 }} (Washington, DC: U.S. Army Corps of Engineers.) Publication No. EP 870-1-67. p. 256.

In 1940 Congress passed a law authorizing the creation of an interstate compact to coordinate water quality management among states in the Potomac basin. Maryland, West Virginia, Pennsylvania, Virginia, and the District of Columbia agreed to establish the Interstate Commission on the Potomac River Basin. The compact was amended in 1970 to include coordination of water supply issues and land use issues related to water quality.ICPRB. [http://www.potomacriver.org/cms/index.php?option=com_content&view=article&id=96&catid=39&Itemid=57 "Potomac Timeline."] {{webarchive|url=https://web.archive.org/web/20110105161359/http://www.potomacriver.org/cms/index.php?option=com_content&view=article&id=96&catid=39&Itemid=57 |date=January 5, 2011 }} Updated 2008-04-15.

File:Potomac green water.JPG in the Potomac River is evident from this bright green water in Washington, D.C., caused by a dense bloom of cyanobacteria, April 2012.]]

Beginning in the 19th century, with increasing mining and agriculture upstream and urban sewage and runoff downstream, the water quality of the Potomac River deteriorated. This created conditions of severe eutrophication. It is said that President Abraham Lincoln used to escape to the highlands on summer nights to escape the river's stench. In the 1960s, with dense green algal blooms covering the river's surface, President Lyndon Johnson declared the river "a national disgrace" and set in motion a long-term effort to reduce pollution from sewage and restore the beauty and ecology of this historic river. One of the significant pollution control projects at the time was the expansion of the Blue Plains Advanced Wastewater Treatment Plant, which serves Washington and several surrounding communities.District of Columbia Water and Sewer Authority. Washington, DC. [http://www.dcwater.com/about/gen_overview.cfm "History of Blue Plains Wastewater Treatment Plant."] {{webarchive|url=https://web.archive.org/web/20150317131913/http://www.dcwater.com/about/gen_overview.cfm |date=March 17, 2015 }} Accessed 2010-09-28. Enactment of the 1972 Clean Water Act led to construction or expansion of additional sewage treatment plants in the Potomac watershed. Controls on phosphorus, one of the principal contributors to eutrophication, were implemented in the 1980s, through sewage plant upgrades and restrictions on phosphorus in detergents.

By the end of the 20th century, notable success had been achieved, as massive algal blooms vanished and recreational fishing and boating rebounded. Still, the aquatic habitat of the Potomac River and its tributaries remain vulnerable to eutrophication, heavy metals, pesticides and other toxic chemicals, over-fishing, alien species, and pathogens associated with fecal coliform bacteria and shellfish diseases. In 2005 two federal agencies, the US Geological Survey and the Fish and Wildlife Service, began to identify fish in the Potomac and tributaries that exhibited "intersex" characteristics, as a result of endocrine disruption caused by some form of pollution.U.S. Fish and Wildlife Service. Annapolis, MD (2009). [http://www.fws.gov/chesapeakebay/pdf/endocrine.pdf "Intersex fish: Endocrine disruption in smallmouth bass."] {{webarchive|url=https://web.archive.org/web/20160303192520/http://www.fws.gov/chesapeakebay/pdf/endocrine.pdf |date=March 3, 2016 }}

On November 13, 2007, the Potomac Conservancy, an environmental group, issued the river a grade of "D-plus", citing high levels of pollution and the reports of "intersex" fish.{{cite news |last=Fahrenthold |first=David A. |title=Potomac Recovery Deemed At Risk |newspaper=The Washington Post |date=November 13, 2007 |url=https://www.washingtonpost.com/wp-dyn/content/article/2007/11/12/AR2007111201814.html |access-date=2007-11-13 |url-status=live |archive-url=https://web.archive.org/web/20110701174301/http://www.washingtonpost.com/wp-dyn/content/article/2007/11/12/AR2007111201814.html |archive-date=July 1, 2011}} Since then, the river has improved with a reduction in nutrient runoff, return of fish populations, and land protection along the river. As a result, the same group issued a grade of "B" for 2017 and 2018.{{cite web |url=http://www.potomacreportcard.org/ |title=Potomac Report Card |publisher=Potomac Conservancy |date=28 March 2018 |access-date=26 March 2019 |archive-date=November 12, 2020 |archive-url=https://web.archive.org/web/20201112015940/https://www.potomacreportcard.org/ |url-status=live}} In March 2019, the Potomac Riverkeeper Network launched a laboratory boat dubbed the "Sea Dog", which will be monitoring water quality in the Potomac and providing reports to the public on a weekly basis;[https://www.washingtonpost.com/local/taking-a-swim-in-the-potomac-weekly-readings-will-reveal-water-quality-and-bacteria-levels/2019/03/19/fa173378-4a71-11e9-b79a-961983b7e0cd_story.html Lang, Marissa J. "Taking a swim in the Potomac? Weekly readings will reveal water quality and bacteria levels"] {{Webarchive|url=https://web.archive.org/web/20200908021241/https://www.washingtonpost.com/local/taking-a-swim-in-the-potomac-weekly-readings-will-reveal-water-quality-and-bacteria-levels/2019/03/19/fa173378-4a71-11e9-b79a-961983b7e0cd_story.html |date=September 8, 2020 }}. 2019-03-30. Retrieved 2019-03-30. in that same month, the catching near Fletcher's Boat House of a Striped Bass estimated to weigh {{convert|35|lb|kg|abbr=on}} was seen as a further indicator of the continuing improvement in the health of the river.[https://wtop.com/local/2019/03/need-a-bigger-boat-35-pound-bass-caught-on-the-potomac-river/ "Need a bigger boat: 35-pound bass caught on the Potomac River"] {{Webarchive|url=https://web.archive.org/web/20190403174718/https://wtop.com/local/2019/03/need-a-bigger-boat-35-pound-bass-caught-on-the-potomac-river/ |date=April 3, 2019 }}. Washington Post. 2019-04-03. Accessed: 2019-04-03.

File:Potomac River Discharge at Little Falls 1931-2017.jpg

The average daily flow during the water years 1931–2018 was {{convert|11,498|cuft|m3}} /s. The highest average daily flow ever recorded on the Potomac at Little Falls, Maryland (near Washington, D.C.), was in March 1936 when it reached {{convert|426,000|cuft|m3}} /s. The lowest average daily flow ever recorded at the same location was {{convert|601.0|cuft|m3}} /s in September 1966 The highest crest of the Potomac ever registered at Little Falls was 28.10 ft, on March 19, 1936;{{cite web |url=https://water.weather.gov/ahps2/crests.php?wfo=lwx&gage=brkm2&crest_type=historic |title=Historic Crests for Potomac near Washington, DC (Little Falls) |date=2019 |publisher=National Weather Service - Water |access-date=23 March 2019 |archive-date=December 7, 2020 |archive-url=https://web.archive.org/web/20201207130734/https://water.weather.gov/ahps2/crests.php?wfo=lwx&gage=brkm2&crest_type=historic |url-status=live}}{{cite web |url=https://www.weather.gov/lwx/1936Flood |title=1936 Flood Retrospective: The Flood of March 17-19 1936 |date=16 March 2016 |website=weather.gov |publisher=NWS |access-date=26 March 2019 |archive-date=December 7, 2020 |archive-url=https://web.archive.org/web/20201207130757/https://www.weather.gov/lwx/1936Flood |url-status=live}}

however, the most damaging flood to affect Washington, DC and its metropolitan area was that of October 1942.{{cite web |url=https://www.history.com/news/worst-flood-washington-dc-world-war-ii-fdr |title=World War II-Era Flood Was the Worst in D.C.'s History |last=Little |first=Becky |date=14 September 2018 |website=HISTORY |publisher=A&E Television Networks, LLC |access-date=23 March 2019 |archive-date=December 7, 2020 |archive-url=https://web.archive.org/web/20201207130817/https://www.history.com/news/worst-flood-washington-dc-world-war-ii-fdr |url-status=live}}

{{multiple image

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| image1 = PR VA MD WV Boundary near Harpers Ferry by USFWS ebm.png

| image2 = Potomac River passing through two water gaps.jpg

| caption1 = Boundary between Maryland, Virginia, and West Virginia at Harpers Ferry {{center| }}

| caption2 = Satellite view of the Potomac River passing through two water gaps downstream of Harpers Ferry

}}

For 400 years Maryland and Virginia have disputed control of the Potomac and its North Branch since both states' original colonial charters grant the entire river rather than half of it as is normally the case with boundary rivers. In its first state constitution adopted in 1776, Virginia ceded its claim to the entire river but reserved free use of it, an act disputed by Maryland. Both states acceded to the 1785 Mount Vernon Compact and the 1877 Black-Jenkins Award which granted Maryland the river bank-to-bank from the low-water mark on the Virginia side while permitting Virginia full riparian rights short of obstructing navigation.

From 1957 to 1996, the Maryland Department of the Environment (MDE) routinely issued permits applied for by Virginia entities concerning the use of the Potomac. However, in 1996 the MDE denied a permit submitted by the Fairfax County Water Authority to build a water intake {{convert|725|ft|m}} offshore, citing potential harm to Maryland's interests by an increase in Virginia sprawl caused by the project. After years of failed appeals within the Maryland government's appeal processes, in 2000 Virginia took the case to the Supreme Court of the United States, which exercises original jurisdiction in cases between two states. Maryland claimed Virginia lost its riparian rights by acquiescing to MDE's permit process for 63 years (MDE began its permit process in 1933). A Special Master appointed by the Supreme Court to investigate recommended the case be settled in favor of Virginia, citing the language in the 1785 Compact and the 1877 Award. On December 9, 2003, the Court agreed in a 7–2 decision.U.S. Supreme Court. Virginia v. Maryland, {{ussc|540|56|2003}}

File:Land Use in the Potomac Basin.gif

The original charters are silent as to which branch from the upper Potomac serves as the boundary, but this was settled by the 1785 Compact. When West Virginia seceded from Virginia in 1863, the question of West Virginia's succession in title to the lands between the branches of the river was raised, as well as title to the river itself. Claims by Maryland to West Virginia land north of the South Branch (all of Mineral and Grant Counties and parts of Hampshire, Hardy, Tucker and Pendleton Counties) and by West Virginia to the Potomac's high-water mark were rejected by the Supreme Court in two separate decisions in 1910.Maryland v. West Virginia, {{ussc|217|1|1910}}Maryland v. West Virginia, {{ussc|217|577|1910}}

File:American Shad by Duane Raver USFWS.jpg

A variety of fish inhabit the Potomac, including bass, muskellunge, pike, walleye. The northern snakehead, an invasive species resembling the native bowfin, lamprey, and American eel, was first seen in 2004.{{cite web|url=http://www.baltimoresun.com/sports/outdoors/bal-md.snakeheads27apr27,0,6241227.story|title=Potomac snakeheads not related to others|archive-url=https://web.archive.org/web/20070930035221/http://www.baltimoresun.com/sports/outdoors/bal-md.snakeheads27apr27,0,6241227.story|archive-date=September 30, 2007|publisher=Associated Press|via=The Baltimore Sun|date=April 27, 2007}}{{cite web |url=https://dwr.virginia.gov/fishing/snakehead/ |title=Northern Snakehead |publisher=Virginia Department of Wildlife Resources |access-date=July 4, 2020 |archive-date=November 12, 2020 |archive-url=https://web.archive.org/web/20201112024553/https://dwr.virginia.gov/fishing/snakehead/ |url-status=live}} Many species of sunfish are also present in the Potomac and its headwaters.{{cite web |url=http://www.potomacriver.org/wp-content/uploads/2014/11/MasterFreshFishList0213.pdf |title=Fishes of the freshwater potomac |author=Jim Cummins |date=2013 |website=www.potomacriver.org |publisher=Interstate Commission on the Potomac River Basin |access-date=February 27, 2018 |archive-date=September 30, 2020 |archive-url=https://web.archive.org/web/20200930154506/http://www.potomacriver.org/wp-content/uploads/2014/11/MasterFreshFishList0213.pdf |url-status=live}} Although rare, bull sharks can be found.{{cite web |url=http://www.somdnews.com/stories/09032010/entetop183727_32296.shtml |title=Sharks! Watermen catch two 8-footers on same day |publisher=somdnews.com |access-date=2011-12-17 |url-status=dead |archive-url=https://archive.today/20120910163457/http://www.somdnews.com/stories/09032010/entetop183727_32296.shtml |archive-date=September 10, 2012}}

After having been depressed for many decades, the river's population of American shad is currently re-bounding as a result of the ICPRB's successful "American Shad Restoration Project" that was begun in 1995. In addition to stocking the river with more than 22 million shad fry, the Project supervised the construction of a fishway that was built to facilitate the passage of adults around the Little Falls Dam on the way to their traditional spawning grounds upstream.{{cite web |url=https://www.potomacriver.org/wp-content/uploads/2014/12/shadfs.pdf |title=THE POTOMAC RIVER AMERICAN SHAD RESTORATION PROJECT |date=March 2014 |website=www.potomacriver.org |publisher=Interstate Commission on the Potomac River Basin |access-date=February 26, 2018 |archive-date=September 30, 2020 |archive-url=https://web.archive.org/web/20200930153116/https://www.potomacriver.org/wp-content/uploads/2014/12/shadfs.pdf |url-status=live}}

{| class="wikitable mw-collapsible mw-collapsed"

|-

! Freshwater fish of the Potomac River

|-

|

• Bowfin Amia calva

• White bullhead catfish Ameiurus catus
• Yellow bullhead catfish Ameiurus natalis
• Brown bullhead catfish Ameiurus nebulosus
• Channel catfish Ictalurus punctatus
• Tadpole madtom Noturus gyrinus
• Margined madtom Noturus insignis
• Blue catfish*Ictalurus furcatus*
• Flathead catfish*Pylodictis olivaris*

• American eel Anguilla rostrata

• Longnose gar Lepisosteus osseus

• Blueback herring Alosa aestivalis
• Hickory shad Alosa mediocris
• Alewife Alosa pseudoharengus
• American shad Alosa sapidissima
• Gizzard shad Dorosoma cepedianum
• Threadfin shad Dorosoma petenense

• Banded killifish Fundulus diaphanus
• Mummichog killifish Fundulus heteroclitus
• Spotfin killifish Fundulus luciae
• Striped killifish Fundulus majalis
• Rainwater killifish Lucania parva

• Sheepshead minnow Cyprinodon variegatus

• Least brook lamprey Lampetra aepyptera
• American brook lamprey Lampetra appendix
• Sea lamprey Petromyzon marinus

• Central stoneroller Campostoma anomalum
• Goldfish Carassius auratus
• Redside dace Clinostomus elongatus
• Rosyside dace Clinostomus funduloides
• Grass carp Ctenopharyngodon idella
• Satinfin shiner Cyprinella analostana
• Spotfin shiner Cyprinella spiloptera
• Common carp Cyprinus carpio
• Cutlips minnow Exoglossum maxillingua
• Eastern silvery minnow Hybognathus regius
• Striped shiner Luxilus chrysocephalus
• Common shiner Luxilus cornutus
• Allegheny pearl dace Margariscus margarita
• River chub Nocomis micropogon
• Golden shiner Notemigonus crysoleucas
• Comely shiner Notropis amoenus
• Emerald shiner Notropis atherinoides
• Bridle shiner Notropis bifrenatus
• Silverjaw minnow Notropis buccatus
• Ironcolor shiner Notropis chalybaeus
• Spottail shiner Notropis hudsonius
• Swallowtail shiner Notropis procne
• Rosyface shiner Notropis rubellus
• Bluntnose minnow Pimephales notatus
• Fathead minnow Pimephales promelas
• Eastern blacknose dace Rhinichthys atratulus
• Longnose dace Rhinichthys cataractae
• Creek chub Semotilus atromaculatus
• Fallfish Semotilus corporalis
• Bluehead chub Nocomis leptocephalus
• Mimic shiner Notropis volucellus

• Eastern mudminnow Umbra pygmaea

• Greenside darter Etheostoma blennioides
• Rainbow darter Etheostoma caeruleum
• Fantail darter Etheostoma flabellare
• Swamp darter Etheostoma fusiforme
• Johnny darter Etheostoma nigrum
• Tessellated darter Etheostoma olmstedi
• Glassy darter Etheostoma vitreum
• Banded darter Etheostoma zonale
• Yellow perch Perca flavescens
• Common logperch Percina caprodes
• Stripeback darter Percina notogramma
• Shield darter Percina peltata
• Walleye Sander vitreum

• Trout-perch Percopsis omiscomaycus

• Redfin pickerel Esox americanus
• Northern pike Esox lucius
• Muskellunge Esox masquinongy
• Chain pickerel Esox niger

• Pirate perch Aphredoderus sayanus

• Eastern mosquitofish Gambusia holbrooki
• Guppy Poecilia reticulata

• Sheepshead minnow Cyprinodon variegatus

• Mottled sculpin Cottus bairdii
• Blue Ridge sculpin Cottus caeruleomentum
• Potomac sculpin Cottus girardi

• Inland silverside Menidia beryllina

• Rainbow smelt Osmerus mordax

• Northern snakehead*Channa argus*

• Shortnose sturgeon Acipenser brevirostrum
• Atlantic sturgeon Acipenser oxyrhinchus

• Quillback Carpiodes cyprinus
• White sucker Catostomus commersoni
• Creek chubsucker Erimyzon oblongus
• Northern hogsucker Hypentelium nigricans
• Golden redhorse Moxostoma erythrurum
• Shorthead redhorse Moxostoma macrolepidotum
• Torrent sucker Thoburnia rhothoeca

• Mud sunfish Acantharcus pomotis
• Rock bass Amblopites rupestris
• Flier sunfish Centrarchus macropterus
• Blackbanded sunfish Enneacanthus chaetodon
• Bluespotted sunfish Enneacanthus gloriosus
• Banded sunfish Enneacanthus obesus
• Redbreast sunfish Lepomis auritus
• Green sunfish Lepomis cyanellus
• Pumpkinseed sunfish Lepomis gibbosus
• Warmouth sunfish Lepomis gulosus
• Bluegill sunfish Lepomis macrochirus
• Longear sunfish Lepomis megalotis
• Redear sunfish Lepomis microlophus
• Smallmouth bass Micropterus dolomieu
• Largemouth bass Micropterus salmoides
• White crappie Pomoxis annularis
• Black crappie Pomoxis nigromaculatus

• White perch Morone americana
• Striped bass Morone saxatilis

• Rainbow trout (Oncorhynchus mykiss)
• Brown trout (Salmo trutta)

  *denotes naturalized species;

Sources:

• [https://web.archive.org/web/20070509065631/http://www.dnr.state.md.us/streams/pubs/fishkey_2003.pdf Dnr.state.md: Fish key of native species]
• http://www.potomacriver.org/wp-content/uploads/2014/11/MasterFreshFishList0213.pdf

|}

{| class="wikitable mw-collapsible mw-collapsed"

|-

! Tidal freshwater fish of the Potomac River

|-

|

Striped mullet Mugil cephalus

Spot Leiostomus xanthurus

Spotted seatrout Cynoscion nebulosus

Atlantic Croaker Micropogonias undulatus

Red drum Sciaenops ocellata

Hogchoker Trinectes maculatus

Bull shark Carcharhinus leucas

Sources:

• [https://web.archive.org/web/20070509065631/http://www.dnr.state.md.us/streams/pubs/fishkey_2003.pdf Dnr.state.md: Fish key of native species]
• http://www.potomacriver.org/wp-content/uploads/2014/11/MasterFreshFishList0213.pdf

|}

File:Bottlenose dolphin with young.JPG

Early European colonists who settled along the Potomac found a diversity of large and small mammals living in the dense forests nearby. Bison, elk, wolves (both gray and red) and cougars were still present at that time, but had been hunted to extirpation by the middle of the 19th century. Among the denizens of the Potomac's banks, beavers and otters met a similar fate, while small populations of American mink and American martens survived into the 20th century in some secluded areas.

There is no record of early settlers having observed marine mammals in the Potomac, but several sightings of Atlantic bottle-nosed dolphins (Tursiops truncatus) were reported during the 19th century. In July 1844, a pod of 14 adults and young was followed up the river by men in boats as high as the Aqueduct Bridge (approximately the same location occupied by Key Bridge today).{{cite web |title=The Mysterious Dolphins of the Potomac |url=https://www.atlasobscura.com/articles/bottlenose-dolphins-potomac-chesapeake |access-date=February 26, 2018 |year=2017 |url-status=live |archive-url=https://archive.today/20170930230141/http://www.atlasobscura.com/articles/bottlenose-dolphins-potomac-chesapeake |archive-date=September 30, 2017}}

Since 2015, perhaps as a result of warmer temperatures, rising water levels in the Chesapeake Bay and improving water quality in the Potomac, unprecedented numbers of Atlantic bottle-nosed dolphins have been observed in the river. According to Dr. Janet Mann of Georgetown University's [http://www.pcdolphinproject.org Potomac-Chesapeake Dolphin Project], more than 500 individual members of the species have been identified in the Potomac during this period.{{cite web |title=Potomac-Chesapeake Dolphin Project |url=http://www.pcdolphinproject.org/research/ |access-date=February 26, 2018 |year=2018 |url-status=live |archive-url=https://web.archive.org/web/20170406105846/http://www.pcdolphinproject.org/research/ |archive-date=April 6, 2017}}

File:Eastern Box Turtle NPS.jpgs are frequently spotted along the towpath of the C&O Canal.]]

File:Fivelined skink.jpg

File:South Branch Potomac River South Branch Depot WV 2004.JPG|The South Branch near South Branch Depot, West Virginia

File:View of Potomac River at Junction of Cacapon River.jpg|Confluence of the Cacapon River (barely visible) with the Potomac

File:Potomac River Water Gaps Harpers Ferry w compass and pointer.jpg|Oblique air photo, facing southwest, of the Potomac River flowing through water gaps in the Blue Ridge Mountains. Virginia on the left, Maryland on the right, West Virginia in upper right, including Harpers Ferry (partially obscured by Maryland Heights of Elk Ridge Mountain) at the confluence of the Potomac and Shenandoah Rivers.

File:Potomac River at Goose Creek.jpg|Potomac River at Goose Creek

File:PR Great Falls of the Potomac aquatint by George Beck 1802.jpg|The Great Falls of the Potomac, viewed from the Virginia bank of the river (Engraving based on an aquatint drawn by George Jacob Beck in 1802)

File:Potomac River at Occonquan Bay.jpg|Potomac near Occoquan Bay

File:PR Georgetown or City of Washington 1801 by Beck.jpg|View of the Potomac River, Analostan Island, Georgetown, and, in the distance, buildings of the nascent City of Washington. (Engraving based on an 1801 watercolor by George Jacob Beck.)

File:Jefferson Memorial.jpg|Jefferson Memorial in Washington, D.C., viewed from across the Tidal Basin of the Potomac

File:The Pentagon US Department of Defense building.jpg|The Pentagon, looking northeast with the Potomac in the distance

File:East Branch of the Potomac 1839 (via xparency) LOC.jpg|East Branch of the Potomac (now called the Anacostia River) near its confluence with the mainstem Potomac in Washington. (Watercolor drawn in 1839 by Augustus Kollner.)

File:View of Potomac River from Mount Vernon.jpg|View of the Potomac from Mount Vernon

File:Potomac Reagan National.jpg|Potomac River seen while landing at Reagan National Airport

File:2016-06-06 16 55 09 View northeast down the North Branch Potomac River from the Gorman-Gormania Bridge (U.S. Route 50) between Gormania, Grant County, West Virginia and Gorman, Garrett County, Maryland.jpg|View northeast down the North Branch Potomac River from the Gorman-Gormania Bridge (U.S. Route 50) between Gormania, Grant County, West Virginia and Gorman, Garrett County, Maryland

File:2016-06-18 07 22 42 View east down the North Branch Potomac River from the Piedmont-Westernport Bridge between Piedmont, Mineral County, West Virginia and Westernport, Allegany County, Maryland.jpg|The North Branch Potomac River near Piedmont, WV

File:Potomac River South Branch Depot WV 2007 05 07 07.jpg|The South Branch Potomac River near South Branch Depot, WV

File:South Branch Potomac River Millesons Mill WV 2007 05 07 01.jpg|The South Branch of the Potomac River at Millesons Mill, WV

File:Map of Potomac River Watershed in West Virginia Virginia Pennsylvania Maryland.jpg|Potomac River Watershed in West Virginia, Virginia, Pennsylvania, and Maryland

• List of cities and towns along the Potomac River
• List of crossings of the Potomac River
• List of islands on the Potomac River
• List of rivers of Maryland
• List of rivers of Virginia
• List of rivers of West Virginia
• List of tributaries of the Potomac River
• List of variant names of the Potomac River
• Potomac Heritage Trail
• Air Florida Flight 90, a flight crashed into Potomac River just after takeoff from Washington National Airport
• 2025 Potomac River mid-air collision, an American Eagle Bombardier CRJ701ER collided with a Sikorsky VH-60M Black Hawk, both crashed into Potomac River on January 29, 2025.

• {{cnote|AQU|The diversion dam at Great Falls, often called the "Aqueduct Dam", was built in the 1850s by the US Army Corps of Engineers as part of the project assigned to them by Congress to supply clean water from above Great Falls to Washington, DC. Water diverted by the dam flows 12 miles through a 9-foot diameter pipeline to Dalecarlia Reservoir on the outskirts of the city where it is first allowed to settle and then filtered and purified before being distributed to consumers. Since 1927, potable water from Dalecarlia has also been provided to Arlington County and some other sections of nearby northern Virginia through three 20-inch diameter pipelines that cross the Potomac under the deck of Chain Bridge. In addition, there is nearby a 4-foot diameter conduit constructed in 1967 that traverses the Potomac beneath the riverbed which is used primarily for backup purposes.[https://archive.today/20180219231327/https://www.washingtonian.com/2007/03/01/water-water/ "Water, Water ... "] by Larry Van Dyne, Washingtonian Magazine (March 2007)[https://archive.today/20180219231922/http://www.virginiaplaces.org/nova/watersourcesnova.html "Sources of Northern Virginia Drinking Water"], Virginia Places }}
• {{cnote|GHL|"Evidence of the ancient Potomac River bed can be seen in well-rounded boulders, smoothed surfaces and grooves, and beautifully formed potholes. Look for sandstone boulders along the trail, which were deposited by massive floods. The sandy soils along the river trail, with shells mixed in, are a result of sediment deposits from floods. Some of the oldest sediment deposits in the area can be found on Glade Hill, between the Matildaville and Carriage Road trails. Glade Hill was once an island in the Potomac River, and the deposits found there were left before Mather Gorge formed."[https://www.nps.gov/grfa/learn/nature/geology.htm Great Falls Geology] {{Webarchive|url=https://web.archive.org/web/20180104015155/https://www.nps.gov/grfa/learn/nature/geology.htm |date=January 4, 2018 }}, National Park Service, April 10, 2015 }}
• {{cnote|PIF|"In the Late Pennsylvanian, the rocks of the Stubblefield Falls domain of the Mather Gorge Formation moved up relative to the Sykesville Formation on the steep, west-dipping Plummers Island fault and mylonite zones (Schoenborn, 2001) within an existing Plummers Island shear zone (figs. 5, 6). Shearing formed S2 cleavage with below-closure muscovite growth and more pervasive S2 cleavage in the Sykesville Formation. By the earliest Permian, all of the rocks in the Potomac terrane had cooled through 235°C (figs. 3, 5). Apatite fission-track data indicate cooling through ≈90°C to 100°C in Early Jurassic to Early Cretaceous time, with increasing ages to the east, suggesting kilometer-scale rotation of the Potomac terrane in the Cretaceous and (or) Tertiary, with the west side up."Michael J. Kunk, et al., [https://pubs.usgs.gov/circ/2004/1264/html/trip5/ Multiple Paleozoic Metamorphic Histories, Fabrics, and Faulting in the Westminster and Potomac Terranes, Central Appalachian Piedmont, Northern Virginia and Southern Maryland] {{Webarchive|url=https://web.archive.org/web/20171231212310/https://pubs.usgs.gov/circ/2004/1264/html/trip5/ |date=December 31, 2017 }}, U.S. Geological Survey, 23 November 2016 }}
• {{cnote|BLK|"Two samples collected from the terrace dissected by Great Falls indicate that the Falls were established in their current location by 30 ky. A series of 6 samples taken from a vertical transect just below the falls, indicates that vertical incision continued a rate of 0.5 m/ky between 27 and 12 ky, increasing to nearly 1.0 m/ky during the Holocene. These data suggest that the drop over Great Falls is growing with time. A dramatic increase in outcrop weathering and soil depth 3.5 km downstream of the Falls, suggests that prior to establishment of the Great Falls knickzone, a similar feature was likely present near Black Pond. 10-Be data are not yet available for this paleo knick zone; however, a 10-Be model age >200 ky from the top of Plummers island 5 km down stream of Black Pond suggests a much older period of retreat led to the formation of the Black Pond paleo knick zone."Paul Bierman, et al., [https://gsa.confex.com/gsa/2004NE/finalprogram/abstract_69763.htm Great Falls is 30,000 Years Old] {{Webarchive|url=https://web.archive.org/web/20080907202524/http://gsa.confex.com/gsa/2004NE/finalprogram/abstract_69763.htm |date=September 7, 2008 }}, Paper No. 35-5, Session No. 35, Geomorphic Process Rates on the Passive Margin, March 26, 2004. Geological Society of America Abstracts with Programs, Vol. 36, No. 2, p. 94}}
• {{cnote|PES|"The Potomac Estuary: From the Chain Bridge in Washington, DC, to Point Lookout at the confluence with the Chesapeake Bay, the Potomac Estuary is a long and narrow estuary—approximately 189 km. With its many tributaries and bays, however, the Potomac Estuary has a shoreline of 1,800 km. The Estuary meanders in a south, southeasterly direction, except for a sharp bend about halfway downriver. The Estuary has three well-defined and distinct zones. The upper zone, from Chain Bridge to Indian Head, is the tidal freshwater reach, with salinities of less than 0.5 parts per thousand (ppt). The middle reach, between Indian Head and the Route 301 Bridge at Morgantown, is the transition zone. The salinity of this zone varies from 0.5 to 7.0 ppt and is often referred to as the zone of maximum turbidity. The lower zone, from the 301 Bridge to Point Lookout, has salinities ranging from 7 to 16 ppt."{{Cite web |url=http://www.potomacriver.org/wp-content/uploads/2015/07/NAJ_01_Chap1.pdf |title=Chapter One: Introduction |access-date=December 30, 2017 |archive-date=December 7, 2020 |archive-url=https://web.archive.org/web/20201207143813/http://www.potomacriver.org/wp-content/uploads/2015/07/NAJ_01_Chap1.pdf |url-status=live}} }}
• {{cnote|TRI|The rocky western (upriver) and central portions of the island are part of the Piedmont Plateau, while the southeastern part is within the Atlantic Coastal Plain. At one point opposite Georgetown, the Atlantic Seaboard fall line between the Piedmont and the Coastal Plain can be seen as a natural phenomenon. The island has about {{convert|2.5|mi|km|adj=on}} of shoreline, and the highest area of the island (where the Mason mansion stood) is about {{convert|44|ft|m}} above sea level.}}

{{reflist|colwidth=30em}}

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• Rice, James D., Nature and History in the Potomac Country: From Hunter-Gatherers to the Age of Jefferson. (2009), Baltimore: Johns Hopkins University Press; {{ISBN|0-8018-9032-2}}; {{ISBN|978-0-8018-9032-1}}
• Smith, J. Lawrence, The Potomac Naturalist: The Natural History of the Headwaters of the Historic Potomac (1968), Parsons, WV: McClain Printing Co.; {{ISBN|0-87012-023-9}}; {{ISBN|978-0-87012-023-7}}

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{{Sister project links|Potomac River}}

• [http://water.weather.gov/ahps/ Advanced Hydrologic Prediction Service] - [https://web.archive.org/web/20150622084034/http://newweb.erh.noaa.gov/ahps2/index.php?wfo=lwx Baltimore/Washington (Sterling, VA)] - including Potomac River levels
• Potomac River level at [http://water.weather.gov/ahps2/hydrograph.php?wfo=lwx&gage=wllm2&view=1,1,1,1,1,1 Williamsport]
• Potomac River level at [http://water.weather.gov/ahps2/hydrograph.php?wfo=lwx&gage=hfew2&view=1,1,1,1,1,1 Harpers Ferry]

{{Potomac River System}}

{{Maryland waters}}

{{Monongahela National Forest}}

{{AHR}}

{{Authority control}}

Category:Rivers of Washington, D.C.

Category:Rivers of Maryland

Category:Rivers of Virginia

Category:Rivers of West Virginia

Category:Monongahela National Forest

Category:History of West Virginia

Category:Borders of Maryland

Category:Borders of Virginia

Category:Borders of West Virginia

Category:American Heritage Rivers

Category:Tributaries of the Chesapeake Bay

Category:West Virginia placenames of Native American origin

Category:National Recreation Trails in Washington, D.C.

Category:National Recreation Trails in Maryland

Category:National Recreation Trails in Virginia

Category:National Recreation Trails in West Virginia