Located in an arid region, Shoshone Falls naturally received most of its water from snowmelt in the Rocky Mountains of Idaho and Wyoming near Yellowstone and Grand Teton National Parks, and to a lesser extent springs in the Snake River Canyon above Twin Falls. A large number of reservoirs, and massive diversions for the irrigation of nearly of farmland, have greatly reduced the volume of water reaching the falls, such that the canyon springs are now the primary water source. The average Snake River flow at the Twin Falls stream gaging station is . For comparison, the average Snake River flow at Idaho Falls – upstream – is . The average flow below Milner Dam, upstream, is just , and is frequently zero in the late summer and fall.