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 2,000,000 acres (810,000 ha) 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 3,530 cubic feet per second (100 m³/s).
For comparison, the average Snake River flow at Idaho Falls – 190 miles (310 km) upstream – is 5,911 cubic feet per second (167.4 m³/s).
The average flow below Milner Dam, 24 miles (39 km) upstream, is just 884 cubic feet per second (25.0 m³/s), and is frequently zero in the late summer and fall.

Idaho Power's Shoshone Falls Dam is located directly upstream from the falls and diverts water to the Shoshone hydroelectric plant, further reducing the water volume.
Idaho Power is required to maintain a minimum daytime "scenic flow" of 300 cubic feet per second (8.5 m³/s) from April through Labor Day, although even this small flow can be difficult to achieve due to a lack of water in the Snake River.
Further complicating the issue is that most irrigation water is needed in the summer, which coincides with the peak tourist season.
The Shoshone power plant draws up to 950 cubic feet (27 m³) of water per second; thus, the flow of the falls will only increase if the Snake River flow exceeds the combined plant capacity and scenic flow requirement.
The best time to view the falls is between April and June, when snowmelt is peaking, and when water is released from upriver reservoirs to assist steelhead migration.

The highest flow ever recorded at Twin Falls was 32,200 cubic feet per second (910 m³/s) on June 10, 1914, and the lowest was 303 cubic feet per second (8.6 m³/s) on April 1, 2013.
On a monthly basis, June generally sees the heaviest flows, at 6,280 cubic feet per second (178 m³/s), and August the lowest flows, 956 cubic feet per second (27.1 m³/s).
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 2,000,000 acres (810,000 ha) 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 3,530 cubic feet per second (100 m³/s). For comparison, the average Snake River flow at Idaho Falls – 190 miles (310 km) upstream – is 5,911 cubic feet per second (167.4 m³/s). The average flow below Milner Dam, 24 miles (39 km) upstream, is just 884 cubic feet per second (25.0 m³/s), and is frequently zero in the late summer and fall.
Idaho Power's Shoshone Falls Dam is located directly upstream from the falls and diverts water to the Shoshone hydroelectric plant, further reducing the water volume. Idaho Power is required to maintain a minimum daytime "scenic flow" of 300 cubic feet per second (8.5 m³/s) from April through Labor Day, although even this small flow can be difficult to achieve due to a lack of water in the Snake River. Further complicating the issue is that most irrigation water is needed in the summer, which coincides with the peak tourist season. The Shoshone power plant draws up to 950 cubic feet (27 m³) of water per second; thus, the flow of the falls will only increase if the Snake River flow exceeds the combined plant capacity and scenic flow requirement. The best time to view the falls is between April and June, when snowmelt is peaking, and when water is released from upriver reservoirs to assist steelhead migration.
The highest flow ever recorded at Twin Falls was 32,200 cubic feet per second (910 m³/s) on June 10, 1914, and the lowest was 303 cubic feet per second (8.6 m³/s) on April 1, 2013. On a monthly basis, June generally sees the heaviest flows, at 6,280 cubic feet per second (178 m³/s), and August the lowest flows, 956 cubic feet per second (27.1 m³/s).
Shoshone Falls