Residents of Southern Idaho, eastern Oregon, northwest Wyoming, and southeast Washington enjoy proximity to one of the West’s most scenic and productive aquatic ecosystems in the Snake River, which flows from its origin its headwaters in Wyoming across the full breadth of Idaho to its mouth near Washington’s Tri-cities. At 1,078 miles long, and with an average discharge over 54,000 cubic feet per second, the Snake River is the largest tributary of the Columbia River and one of our nation’s greatest hydrologic resources.

Snake River and Major Tributaries



Rising from tiny headwaters in Grand Teton and Yellowstone National Parks, the Snake flows into Jackson Lake, then through Jackson Hole between the Teton Range and the Continental Divide. After leaving the Upper Snake River Canyon, it receives the Hoback and Greys Rivers before entering Palisades Reservoir in Idaho, where it is met by the Salt River. Below Palisades Dam, the “South Fork” of the Snake empties onto the Snake River Plain, a vast physiographic province extending through southern Idaho across the massif of the Rocky Mountains and underlain by the Snake River Aquifer — one of the most productive aquifers in the United States. Southwest of Rexburg, the Snake receives the North (“Henry’s”) Fork, becoming the “Main Stem” Snake before flowing through downtown Idaho Falls and rounding Fort Hall Indian Reservation before entering American Falls Reservoir. Resuming its westward journey, the river drops over Shoshone Falls – the historical upriver limit of migrating salmon – and passes through Twin Falls en route to Boise.

After passing within 30 miles of Boise, the main river meets the Owyhee, Boise, and Payette Rivers, then defines the roughly 200-mile-long Idaho-Oregon state border as it heads north. The border follows the river into the rugged portion known as “Hells Canyon,” where the Hells Canyon, Oxbow, and Brownlee Dams harness its power. The Salmon River is the Snake’s largest tributary and meets the river in Hells Canyon. From there, the Snake crosses into Washington and Idaho, receiving the Grande Ronde River and then the Clearwater River at Lewiston – the uppermost major city on the navigable stretch of the Snake. As the river leaves Hells Canyon and spreads into the low-lying Palouse Hills of eastern Washington, the Lower Snake River Project’s four dams transform the lower Snake River into a series of reservoirs. The powerful, steep flow of the Snake has been utilized since the 1890s to generate hydroelectricity, allow navigation, and provide irrigation water from a total of fifteen major dams that transform the lower river into a series of reservoirs, several of which have been proposed for removal to restore the river’s once-tremendous salmon runs.

As it passes over the Snake Plain Aquifer on its journey westward to the Columbia River, the Snake flows through pine forests, vast plains, and red rock canyons, exemplifying the region’s rich diversity of landscapes. From Henry’s Fork to Hells Canyon, visiting recreationists have access to incredibly diverse outdoor opportunities as the river morphs from its alpine headwater sources into freestone, whitewater, reservoir, and classic tailwater forms. According to the U.S. Travel Association, Idaho’s $3.4 billion tourism industry employs more than 26,000 Idahoans and generates almost $500 million in local, state, and federal tax revenues. Emergent threats to tributaries join dams, agriculture, pollution, industry, and development to place the health of the Snake, its tributaries, and the downstream Columbia River at great risk.

Snake River Waterkeeper’s jurisdiction includes the totality of the Snake River Basin, from the headwaters in Yellowstone, Wyoming, and Grand Teton National Parks to its confluence with the Columbia River. Our exclusive focus on the health of the Basin as a whole places Snake River Waterkeeper in a unique position to understand threats to the river system and advocate for meaningful improvement to state, regional, and federal policies affecting the Basin while also addressing discrete issues pertaining to local rivers, streams, and sub-basins.