Snake River, a major river of the northwestern United States and the largest tributary of the Columbia River. It begins in Wyoming in Yellowstone National Park and flows some 1,000 miles (1,600 km) to the Columbia near Pasco, Washington. The Snake River system drains most of Idaho and parts of Wyoming, Utah, Nevada, Oregon, and Washington. Tributaries include the Henrys Fork, Big Wood, Boise, Owyhee, Payette, Salmon, and Clearwater rivers.

Throughout much of its course the Snake has carved deep canyons and gorges. The most spectacular is Hells Canyon on the Idaho-Oregon border. With a maximum depth of 7,900 feet (2,400 m), it is the deepest canyon in North America. In southern Idaho the river is marked by numerous falls, most impressive of which is 212–foot (65-m) Shoshone Falls.

The Snake River is an important source of water for irrigation and for hydroelectric power, and is the site of a number of dams. Cities on or near the Snake include Idaho Falls, Pocatello, Twin Falls, Boise, and Lewiston, all in Idaho. Lewis and Clark discovered the river in 1805.