Water resource region

! scope="col" | Region HUC{{cite web|vauthors=McManamay RA, Bevelhimer MS, Kao SC, Yaxing W, Martinez-Gonzalez M, Samu N|title=National Hydropower Asset Assessment Environmental Attribution|url=http://nhaap.ornl.gov/content/environmental-attribution|publisher=USGS-Oak Ridge National Laboratory|access-date=2016-10-12|publication-date=2013}} {{PD-notice}}

! scope="col" | Region name

! scope="col" | Region description{{cite web|title=Boundary Descriptions and Names of Regions, Subregions, Accounting Units and Cataloging Units|url=https://water.usgs.gov/GIS/huc_name.html|publisher=USGS|access-date=2015-11-28}} {{PD-notice}}

! scope="col" | Region location

! scope="col" | Region size

! scope="col" | Region population

! scope="col" | Region map

! scope="row" | 01

| align="center" | New England region

1. the Bay of Fundy
2. the Atlantic Ocean within and between the states of Maine and Connecticut
3. Long Island Sound north of the New York-Connecticut state line
4. the Riviere St. Francois, a tributary of the Saint Lawrence River

| Includes all of Maine, New Hampshire and Rhode Island, and parts of Connecticut, Massachusetts, New York, and Vermont.

! scope="row" | 02

| align="center" | Mid Atlantic region

1. the Atlantic Ocean within and between the states of New York and Virginia
2. Long Island Sound south of the New York-Connecticut State Line
3. the Riviere Richelieu, a tributary of the Saint Lawrence River

| Includes all of Delaware and New Jersey and the District of Columbia, and parts of Connecticut, Maryland, Massachusetts, New York, Pennsylvania, Vermont, Virginia, and West Virginia.

! scope="row" | 03

| align="center" | South Atlantic–Gulf region

1. the Atlantic Ocean within and between the states of Virginia and Florida
2. the Gulf of Mexico within and between the states of Florida and Louisiana
3. the associated waters

| Includes all of Florida and South Carolina, and parts of Alabama, Georgia, Louisiana, Mississippi, North Carolina, Tennessee, and Virginia.

! scope="row" | 04

| align="center" | Great Lakes region

1. the Great Lakes system, including the lake surfaces, bays, and islands
2. the Saint Lawrence River to the Riviere Richelieu drainage boundary.

| Includes parts of Illinois, Indiana, Michigan, Minnesota, New York, Ohio, Pennsylvania, and Wisconsin.

! scope="row" | 05

| align="center" | Ohio region

! scope="row" | 06

| align="center" | Tennessee region

! scope="row" | 07

| align="center" | Upper Mississippi region

! scope="row" | 08

| align="center" | Lower Mississippi region

1. the Mississippi River below its confluence with the Ohio River, excluding the Arkansas, Red, and White River Basins above the points of highest backwater effect of the Mississippi River in those basins
2. coastal streams that ultimately discharge into the Gulf of Mexico from the Pearl River Basin boundary to the Sabine River and Sabine Lake drainage boundary.

| Includes parts of Arkansas, Kentucky, Louisiana, Mississippi, Missouri, and Tennessee.

! scope="row" | 09

| align="center" | Souris-Red-Rainy region

! scope="row" | 10

| align="center" | Missouri region

1. the Missouri River Basin
2. the Saskatchewan River Basin
3. several small closed basins.

| Includes all of Nebraska and parts of Colorado, Iowa, Kansas, Minnesota, Missouri, Montana, North Dakota, South Dakota, and Wyoming.

! scope="row" | 11

| align="center" | Arkansas-White-Red region

! scope="row" | 12

| align="center" | Texas-Gulf region

! scope="row" | 13

| align="center" | Rio Grande region

1. the Rio Grande Basin
2. the San Luis Valley, North Plains, Plains of San Agustin, Mimbres River, Estancia, Jornada Del Muerto, Tularosa Valley, Salt Basin, and other closed basins.

| Includes parts of Colorado, New Mexico, and Texas.

! scope="row" | 14

| align="center" | Upper Colorado region

1. the Colorado River Basin above the Lee Ferry compact point which is one mile below the mouth of the Paria River
2. the Great Divide closed basin.

| Includes parts of Arizona, Colorado, New Mexico, Utah, and Wyoming.

! scope="row" | 15

| align="center" | Lower Colorado region

1. the Colorado River Basin below the Lee Ferry compact point which is one mile below the mouth of the Paria River
2. streams that originate within the United States and ultimately discharge into the Gulf of California
3. the Animas Valley, Willcox Playa, and other smaller closed basins.

| Includes parts of Arizona, California, Nevada, New Mexico, and Utah.

! scope="row" | 16

| align="center" | Great Basin region

! scope="row" | 17

| align="center" | Pacific Northwest region

1. the Strait of Georgia and of Strait of Juan de Fuca
2. the Pacific Ocean within the states of Oregon and Washington; and that part of the Great Basin whose discharge is into the state of Oregon.

| Includes all of Washington and parts of California, Idaho, Montana, Nevada, Oregon, Utah, and Wyoming.

! scope="row" | 18

| align="center" | California region

! scope="row" | 19

| align="center" | Alaska region

! scope="row" | 20

| align="center" | Hawaii region

! scope="row" | 21

| align="center" | Caribbean region

1. the Commonwealth of Puerto Rico
2. the Virgin Islands of the United States
3. other United States Caribbean outlying areas.

| Includes land areas over which the United States has some degree of interest, jurisdiction, or sovereignty.

! scope="row" | 22

| align="center" | South Pacific region