Snake, river, 1,038 mi (1,670 km) long, NW United States, the chief tributary of the Columbia; once called the Lewis River. The Snake rises in NW Wyoming, in Yellowstone National Park, flows through Jackson Lake in Grand Teton National Park, then S and W into Idaho and northwest to its junction with the Henrys Fork River. The combined stream runs southwest, then northwest, crossing southern Idaho through the Snake River plain; there are several notable falls. The Snake makes a bend into Oregon and turns north to form the Idaho-Oregon and Idaho-Washington lines (receiving several tributaries, including the Boise and Salmon rivers), then turns at Lewiston, Idaho (at the mouth of the Clearwater River), and flows generally west to join the Columbia River near Pasco, Wash. Hell's Canyon is the greatest of the Snake's many gorges and one of the deepest in the world. Extending c.125 mi (200 km) N along the Oregon-Idaho line, it reaches a maximum depth of c.7,900 ft (2,410 m).
The Snake was explored by the Lewis and Clark expedition (1803–6) and was of major importance in U.S. expansion into the Pacific Northwest. The river is a major source of electricity, having numerous hydroelectric power plants. The upper and middle courses of the Snake and its tributaries are much used for irrigation by private projects (one of the most notable being at Twin Falls) and by projects of the U.S. Bureau of Reclamation, including the Minidoka project, the Boise project, the Palisades project, and the Owyhee project. Four navigation and hydroelectric power projects along the lower Snake provide slack water navigation from the mouth of the Snake 140 mi (225 km) upstream to Lewiston, Idaho. The projects are linked with the navigation system on the Columbia River. The late 1990s brought efforts to restore portions of the river by removing gravel and establishing new islands.