South Fork Alsea River

{{Use American English|date=February 2025}}

{{Infobox river

| name = South Fork Alsea River

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| name_etymology = Alsi, said to be a corruption of Alsea for native people who lived near the mouth of the river{{cite book | last = McArthur | first = Lewis A. |author2=McArthur, Lewis L. | title = Oregon Geographic Names|edition=7th | publisher = Oregon Historical Society Press | year = 2003 |origyear=1928| location = Portland, Oregon | pages = 19–20| isbn = 0-87595-277-1}}

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| pushpin_map = USA Oregon

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| pushpin_map_caption= Location of the mouth of South Fork Alsea River in Oregon

| subdivision_type1 = Country

| subdivision_name1 = United States

| subdivision_type2 = State

| subdivision_name2 = Oregon

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| subdivision_type4 = County

| subdivision_name4 = Lane and Benton

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| source1 = Central Oregon Coast Range

| source1_location = northeast of Horton, Lane County

| source1_coordinates= {{coord|44|14|49|N|123|25|44|W|display=inline}}{{cite web|title = South Fork Alsea River| work = Geographic Names Information System |url = {{gnis3|1149920}}|publisher = United States Geological Survey (USGS)|date = November 28, 1980|accessdate = November 16, 2015}}

| source1_elevation = {{convert|1721|ft|abbr=on}}Source elevation derived from Google Earth search using GNIS source coordinates.

| mouth = Alsea River

| mouth_location = near Alsea, Benton County

| mouth_coordinates = {{coord|44|22|34|N|123|36|09|W|display=inline,title}}

| mouth_elevation = {{convert|282|ft|abbr=on}}

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The South Fork Alsea River is a tributary of the Alsea River in the U.S. state of Oregon. It begins at northeast of Horton on the east side of the Central Oregon Coast Range and flows generally northwest to near Alsea. There it joins the North Fork Alsea River to form the main stem.{{cite web|title=United States Topographic Map|url=http://mapper.acme.com/?ll=44.376111,-123.602778&z=12&t=T&marker0=44.376111,-123.602778,User%3AFinetooth%2FSandbox6|via=|accessdate=November 16, 2015}}

Fishing in Oregon describes the South Fork as "fair-sized" stream with an average width of {{convert|40|ft|m}}. Fishing for wild cutthroat trout is "excellent", and the stream also supports a population of steelhead.{{cite book|last=Sheehan|first=Madelynne Diness|title=Fishing in Oregon: The Complete Oregon Fishing Guide|edition=10th|publisher=Flying Pencil Publications|location=Scappoose, Oregon|page=7|isbn=0-916473-15-5}} The Bureau of Land Management (BLM) oversees much of the territory through which the river flows.

Alsea Falls Recreation Area, managed by the BLM, is along the river. Open from May 1 through October 31, it has campsites and day-use sites with tent pads, fire rings, picnic tables, toilets, and drinking water. Hiking trails from the recreation area through the forest lead to several waterfalls. The nearby Fall Creek Trail system for mountain bikes has {{convert|6.5|mi|km}} of forested routes for all skill levels.{{cite web|title=Alsea Falls Recreation Area|url=http://www.blm.gov/or/resources/recreation/site_info.php?siteid=220|publisher=Bureau of Land Management|accessdate=November 16, 2015}}