Looking downstream onto Hells Canyon Reservoir

The Snake River is the largest tributary of the Columbia River. It drains over 108,000 square miles in mainly Idaho and portions of Montana, Nevada, Oregon, Washington, and Wyoming. The climate of much of the Snake River watershed is arid or semi-arid and spring snowmelt contributes substantially to the river’s flow. The river’s flow is managed for agriculture, hydropower, flood-control, and recreation using a series of 22 federal and private dams built between 1901 and 1982. The reservoirs, formed by these dams, vary in their construction and management resulting in a range of impacts on the hydrology, biogeochemistry, and ecology of the Snake River.