South Fork of the Snake River

The South Fork of the Snake River is the principal eastern Idaho reach of the Snake River, extending from the outlet of Palisades Reservoir downstream to its confluence with Henrys Fork near Menan, where the two forks join to form the main stem of the Snake. Below Palisades Dam the South Fork flows northwest through Swan Valley, cutting a corridor through public lands managed by the U.S. Forest Service and the Bureau of Land Management. The broader Snake River is the largest tributary of the Columbia River, approximately 1,080 miles long, rising in Yellowstone National Park in Wyoming and flowing through Idaho, Oregon, and Washington before joining the Columbia near the Tri-Cities. The Snake drains about 87 percent of Idaho, and its discharge is dominated by Rocky Mountain snowmelt — peak flows occur in late spring and early summer, with the lowest flows in autumn. The South Fork is regulated by Palisades Dam, a Bureau of Reclamation facility that stores water for the region's extensive downstream irrigation network. The reach supports one of the most significant native Yellowstone cutthroat trout populations remaining in the Snake River basin, alongside non-native brown and rainbow trout, and is managed under federal land designations that prioritize the river's ecological and recreational values.