The Snake River is a major river in the central part of the Pacific Northwest region of the United States. It is about 1,080 miles (1,740 km) long and is the largest tributary of the Columbia River, which is the largest North American river that flows into the Pacific Ocean. The river begins in Yellowstone National Park in western Wyoming and flows across the dry Snake River Plain in southern Idaho, the steep Hells Canyon on the borders of Idaho, Oregon, and Washington, and the rolling Palouse Hills in southeast Washington. It joins the Columbia River just downstream from the Tri-Cities, Washington, in the southern Columbia Basin.
The river’s watershed, which drains parts of six U.S. states, is located between the Rocky Mountains to the north and east, the Great Basin to the south, and the Blue Mountains and Oregon high desert to the west. The region has a long history of volcanic activity. Millions of years ago, basalt rock layers covered large areas of the western Snake River watershed, and the Snake River Plain was shaped by the Yellowstone volcanic hotspot. The river was also changed by massive floods during the most recent Ice Age, which created features such as the Snake River Canyon and Shoshone Falls.
The Snake River once supported some of the largest North American populations of salmon and other anadromous fish, which swim from the ocean to rivers to spawn. For thousands of years, salmon fishing was important in the culture and food of indigenous peoples. The Shoshone and Nez Perce were among several tribes that lived along the river by the early 1800s. In 1805, Lewis and Clark became the first non-natives to see the river while searching for a route from the eastern U.S. to the Pacific. Fur trappers explored more of the area, and their activities caused beaver populations to almost disappear as Americans and British competed for control of the Oregon Territory.
Although early travelers on the Oregon Trail avoided the dry and rocky Snake River region, many settlers arrived after gold was discovered in the 1860s, leading to years of conflict and the forced movement of tribes to reservations. By the early 1900s, large irrigation projects were built along the Snake River, transforming desert areas in south-central Idaho into farmland, which earned the nickname "Magic Valley." Many hydroelectric dams were also built, and four navigation dams on the lower river created a shipping channel to Lewiston, Idaho, the farthest inland port on the West Coast.
Although dam construction, commercial fishing, and other human activities have greatly reduced the numbers of anadromous fish since the late 1800s, the Snake River watershed remains an important habitat for these fish. The Snake River and its tributary, the Salmon River, host the longest sockeye salmon run in the world, with fish traveling 900 miles (1,400 km) from the Pacific to Redfish Lake in Idaho. Since the 1950s, government groups, tribal leaders, and companies have spent a lot of money on fishery restoration and hatchery programs, but with only limited success. The suggestion to remove four lower Snake River dams to help fish travel is a major discussion that continues in the Pacific Northwest.
Course
The Snake River begins near the southern edge of Yellowstone National Park, just north of Two Ocean Pass in the Rocky Mountains of Wyoming. It starts at about 9,200 feet (2,800 meters) above sea level and flows west through the Teton Wilderness. The river meets the Lewis River and continues south into Jackson Lake in Grand Teton National Park. Jackson Lake is a natural lake formed by glaciers, and its size has increased due to the Jackson Lake Dam. Below the dam, the river is joined by Pacific Creek and Buffalo Fork before flowing through Jackson Hole, a valley between the Teton Range to the west and the Gros Ventre Range to the east.
After passing through the town of Jackson, the river forms the Snake River Canyon in Wyoming. It then turns west and enters Idaho, where the Palisades Dam creates Palisades Reservoir. From there, the river flows northwest through Swan Valley and joins the Henrys Fork, which is sometimes called the "North Fork" of the Snake River. The part of the Snake River above this meeting point is sometimes called the "South Fork."
The river then moves southwest across the Snake River Plain, passing through Idaho Falls. It receives water from the Blackfoot River and flows into the American Falls Reservoir, formed by the American Falls Dam. The river turns west again, passing through Minidoka Dam and Milner Dam, where water is used for farming. Below Milner Dam, the river enters the Snake River Canyon in Idaho, where it narrows and forms rapids and waterfalls. Between Milner Dam and the Malad River near Hagerman Fossil Beds National Monument, the river drops 1,300 feet (400 meters) over several waterfalls, including Shoshone Falls, which is 212 feet (65 meters) high. Idaho Power operates hydroelectric plants along this section.
The river continues west, passing through C. J. Strike Reservoir and joining the Bruneau River. It then flows through the Morley Nelson Snake River Birds of Prey National Conservation Area and enters farmland in Idaho's Treasure Valley. The river passes 30 miles (48 kilometers) west of Boise, briefly crosses into Oregon, and turns north to form the Oregon–Idaho border. It is joined by several rivers, including the Boise, Owyhee, Malheur, Payette, Weiser, Powder, and Burnt Rivers.
The river enters Hells Canyon, a deep canyon between Idaho's Rocky Mountains and Oregon's Blue Mountains. The Hells Canyon Hydroelectric Complex includes Brownlee, Oxbow, and Hells Canyon Dams. Since 1967, Hells Canyon Dam has blocked salmon from swimming upstream beyond it, though historically, salmon reached Shoshone Falls.
After leaving Hells Canyon Dam, the river flows through the Hells Canyon Wilderness, where it is difficult to access by land and has strong rapids. Today, the area is popular for activities like whitewater boating and fishing. Hells Canyon is one of the deepest canyons in North America, nearly one-third deeper than the Grand Canyon. The river is joined by the Imnaha River and its longest tributary, the Salmon River, before forming the Idaho–Washington border and receiving the Grande Ronde River.
At Asotin, Washington, the river flows north to Lewiston, Idaho, where it meets the Clearwater River, its largest tributary. The river then turns west into Washington, flowing through the Palouse Hills. Near Lyons Ferry State Park, it is joined by the Tucannon River and the Palouse River, which forms Palouse Falls about 8 miles (13 kilometers) upstream.
The Lower Snake River Project includes four dams—Lower Granite, Little Goose, Lower Monumental, and Ice Harbor—that create lakes to allow barges to travel between the Columbia River and the Port of Lewiston. The Snake River empties into the Columbia River at Burbank, Washington, southeast of the Tri-Cities. This confluence is on Lake Wallula, a reservoir behind McNary Dam on the Columbia River, which is 341 feet (104 meters) above sea level.
The U.S. Army Corps of Engineers has measured the Snake River's flow at Ice Harbor Dam since 1962. Between 1962 and 2023, the average yearly flow was 49,580 cubic feet per second (1,404 cubic meters per second). The highest daily flow recorded was 305,000 cubic feet per second (8,600 cubic meters per second) on June 19, 1974, and the lowest was 2,000 cubic feet per second (57 cubic meters per second) on November 29, 1961. A major flood in 1894 reached an estimated peak of 409,000 cubic feet per second (11,600 cubic meters per second). The Snake River is the 12th largest river in the United States and contributes about one-fifth of the Columbia River's total outflow into the Pacific Ocean.
The river's flow peaks in late spring and early summer due to melting snow in the Rocky Mountains and drops in the fall. Even with dams, the river's flow into the Columbia remains seasonal. At Ice Harbor Dam, the average monthly flow is highest in May and June at over 100,000 cubic feet per second (2,800 cubic meters per second) and lowest in September and October at less than 25,000 cubic feet per second (710 cubic meters per second). Annual flow varies, with a record high of 86,240 cubic feet per second (2,442 cubic meters per second) in 1965 and a low of 27,890 cubic feet per second (790 cubic meters per second) in 1997.
In southern Idaho, the Snake River's flow is influenced by the Eastern Snake River Plain Aquifer, a large underground water storage system in porous volcanic rock. Water from the Snake River is absorbed into the aquifer and re-emerges as springs in the Snake River Canyon. Water from underground rivers and irrigation runoff also flows through the aquifer to the Snake River. Major springs near American Falls and Thousand Springs (near Hagerman, Idaho) help keep the river flowing even during dry summers. At King Hill, about 50 miles (80 kilometers) northwest of Twin Falls, the river's flow remains around 10,000 cubic feet per second (280 cubic meters per second) most of the year, increasing by about 20% during snowmelt and decreasing by about 20% during summer irrigation.
Although the Snake River is long, most of its water is collected in the lower one-fourth of its course. By the time it reaches Hells Canyon Dam, 247 miles (398 kilometers) from its mouth, the average yearly flow is about 19,000 cubic feet per second (
Watershed
The Snake River watershed covers 107,500 square miles (278,000 km²). It drains about 87% of Idaho, 18% of Washington, and 17% of Oregon, as well as small parts of Wyoming, Utah, and Nevada. The eastern edge of the watershed follows the Continental Divide from Lost Trail Pass near Salmon, Idaho, to Tri-Basin Divide near Afton, Wyoming. Since the Continental Divide also forms the Idaho–Montana border south of Lost Trail Pass, the Snake River watershed touches Montana but does not extend into it. The Snake River drains the largest area of any Columbia River tributary, covering about 40% of the entire Columbia River watershed. Compared to the Columbia River above their meeting point, the Snake River is about 180 miles (290 km) longer and drains a similar area, though the Columbia River carries more than twice as much water.
The Snake River watershed is very mountainous. The northern two-thirds include large mountain ranges in the Rocky Mountains, such as the Salmon River Mountains in central Idaho and the Bitterroot Range along the Idaho–Montana border. The Blue Mountains form much of the western boundary of the watershed in southeast Washington and Oregon. To the south are smaller, isolated mountain ranges in the Basin and Range Province, like the Independence and Albion Mountains. To the east are more Rocky Mountain ranges, including the Tetons and the Wind River Range, which includes Gannett Peak, the highest point in the Snake River basin at 13,816 feet (4,211 m). The southern part of the watershed has many volcanic features, such as lava fields and thermal springs, from Craters of the Moon National Monument near Twin Falls to Yellowstone. Ancient lava flows from the Columbia River basalts underlie the western part of the watershed. The Snake River Plain is the largest area without mountains, but it has rugged terrain with canyons carved by the Snake River and its tributaries.
Precipitation across the entire watershed averages 14 inches (360 mm) annually, with most falling as snow at higher elevations. Snowmelt is the main source of runoff. Jackson Hole, Wyoming, has an alpine climate with about 30 inches (760 mm) of rain and 252 inches (6,400 mm) of snow. January is the coldest month, averaging 13°F (−11°C), and July is the warmest, averaging 57.7°F (14.3°C). Twin Falls has a semi-arid climate, with about 9 inches (230 mm) of rain and 13 inches (330 mm) of snow. January averages 29.4°F (−1.4°C), and July averages 73.1°F (22.8°C). The Columbia Basin near the river’s mouth also has a semi-arid climate, with about 10 inches (250 mm) of rain and 5 inches (130 mm) of snow. January averages 34.3°F (1.3°C), and July averages 74.6°F (23.7°C).
About 50% of the watershed is covered by semi-arid shrubland and rangeland, with natural vegetation mainly sagebrush mixed with wheatgrasses and bunchgrasses. About 30% is farmland, with irrigated crops like potatoes, sugar beets, onions, cereal grains, and alfalfa on the Snake River Plain. The Palouse Hills in the northwest focus on dryland wheat and legumes. About 15% is forested, divided into two temperate coniferous forest regions: the South Central Rockies, with Douglas fir, Engelmann spruce, subalpine fir, and lodgepole pine, and the North Central Rockies, with mountain hemlock, white spruce, alpine fir, and western larch. About 4% is barren desert, and about 1% is urbanized.
Most of the watershed is public land, managed by the U.S. Forest Service. National Forests like Nez Perce, Clearwater, Bitterroot, Umatilla, Wallowa–Whitman, Payette, Boise, Salmon–Challis, Sawtooth, Caribou–Targhee, and Bridger–Teton cover much of the northern and eastern parts. These forests include wilderness areas such as Sawtooth, Selway–Bitterroot, Frank Church-River of No Return, Gospel Hump, Hells Canyon, Teton, and Gros Ventre. National Park Service land includes Craters of the Moon National Monument, Yellowstone, and Grand Teton National Parks. Large areas of privately owned farmland are concentrated in the Snake River Plain and Palouse, though most of the Snake River Plain is Bureau of Land Management land.
The Snake River watershed borders several other major North American watersheds. To the south, it borders the endorheic Great Basin, including the area draining to Utah’s Great Salt Lake. To the east, it borders the Green River (part of the Colorado River system, which drains to the Sea of Cortez) and the Yellowstone and upper Missouri Rivers (part of the Mississippi River system, which drains to the Gulf of Mexico). To the north, it borders the Clark Fork and Spokane Rivers, both part of the Columbia River system. To the northwest, it borders other Columbia River tributaries, including those of the John Day and Umatilla Rivers.
Fifty-four named tributaries of the Snake River drain more than 100 square miles (260 km²). Of these, twelve drain areas larger than 2,000 square miles (5,200 km²).
Geology
Over millions of years, the Snake River's current path formed by connecting different drainage systems that were once separate. Much of what is now the Pacific Northwest was once under shallow seas until it rose about 60 million years ago. The ancestral Columbia River began flowing into the Pacific about 40 million years ago. By about 17 million years ago, the "Salmon-Clearwater River," which is now the lower Snake River, flowed west into the Columbia River and then to the Pacific. Another ancient river system drained the western part of the Snake River Plain. Some scientists think this river flowed south of the Blue Mountains, while others believe it went toward Northern California. The Columbia River basalts, a series of large volcanic eruptions that covered the Columbia Basin and surrounding areas, changed the landscape and erased most evidence of older river channels starting about 17 million years ago. The first basalt flows pushed the ancient Salmon-Clearwater River much farther north than it is today.
About 12–10 million years ago, the Blue Mountains region began rising, lifting basalt layers to form a plateau. Between 11–9 million years ago, movement of the Earth's crust linked to the Yellowstone hotspot caused the western part of the Snake River Plain near Boise to sink, creating a valley between two fault zones. This blocked the ancient Snake River, causing water to collect and form Lake Idaho about 10 million years ago. The eastern part of the Snake River Plain formed as the North American Plate moved west over the Yellowstone hotspot. Rising magma created highlands similar to the modern Yellowstone plateau and left behind large basalt flows.
As the Yellowstone hotspot moved east, the land behind it sank, creating the depression of the eastern Snake River Plain. This movement shifted the Continental Divide eastward. Before the eastern Snake River Plain formed, the area east of Arco, Idaho—now the headwaters of the Snake River—flowed toward the Atlantic Ocean via the Mississippi River. About 4.5 million years ago, the shifting Continental Divide changed the direction of water flow, sending it west into Lake Idaho. This change was shown by rising water levels in Lake Idaho at that time. The Snake River drainage system expanded eastward toward what is now Yellowstone National Park. During this expansion, the Snake River captured the Bear River, which was later redirected to its modern outlet in the Great Salt Lake Basin about 50,000 to 60,000 years ago by lava flows in southeast Idaho.
In the Columbia Basin about 10.5 million years ago, the Elephant Mountain basalt eruption forced the Salmon-Clearwater River into its current path through southeast Washington. By 8.5 million years ago, the Salmon-Clearwater River was established in the Columbia River's modern path through Wallula Gap, though the Columbia River still flowed west, closer to the Cascades south of Yakima. The last Columbia River basalt flows occurred about 6 million years ago, by which time the modern confluence of the Columbia and Salmon-Clearwater Rivers was formed, with their combined flow passing through Wallula Gap. About 2.5 million years ago, Lake Idaho reached its highest level, 3,600 feet above modern sea level, and overflowed northward into the Salmon-Clearwater drainage near present-day Huntington, Oregon. Over two million years, this outflow carved Hells Canyon, emptying Lake Idaho and uniting the upper Snake and Salmon-Clearwater Rivers into one system.
The Teton Range, a key feature of the modern Snake River headwaters, began rising about 10 million years ago as the Teton Fault moved, lifting the mountain block while surrounding land dropped. About 2 million years ago, the Hoback Fault formed east of the Tetons, creating a graben valley between the Hoback and Teton faults, forming Jackson Hole. As the valley sank, water filled it to create Lake Teewinot, which drained east into the Green River–Colorado River system. About 1 million years ago, the Snake River captured the Jackson Hole watershed, redirecting Lake Teewinot's drainage to the Snake River and connecting the modern Snake headwaters to the rest of the river. This area was shaped by Ice Age glaciers. Starting about 200,000 years ago, the Buffalo glaciation filled Jackson Hole to a depth of 2,000 feet. Smaller glaciers, such as the Bull Lake and Pinedale glaciations, carved the Tetons into their current shape and formed lake basins, including modern-day Jackson Lake.
While the Snake River's path beyond Jackson Hole was not directly affected by glaciers, its landscape was changed by Ice Age flooding. About 30,000 years ago, the Great Salt Lake Basin was filled with water to form Lake Bonneville, about the size of modern-day Lake Michigan. About 15,000 years ago, the collapse of a natural barrier at Red Rock Pass released massive amounts of water from Lake Bonneville into the Snake River Plain. This flood was 500 times larger than the largest recorded flood at Idaho Falls and dramatically reshaped the Snake River Plain, creating the Snake River Canyon, waterfalls, boulders, cliffs, and coulees. The floodwaters then flowed through Hells Canyon. However, most evidence of these floods was later erased by the even larger Missoula Floods, which occurred in the same period. These floods, caused by the collapse of an ice dam in western Montana, sent water back into the lower Snake River from the north, reaching as far upstream as Lewiston. The Palouse River was redirected to flow south into the Snake River, forming Palouse Falls, whose deep plunge pool shows the power of these floods.
History
Around the end of the last ice age, the Snake River Plain was home to early people known as hunter-gatherers from the Clovis (10,000–9,000 BCE), Folsom (9,000–8,000 BCE), and Plano (8,600–5,800 BCE) cultures. In Washington, the Marmes Rockshelter along the lower Snake River was flooded in 1968 after a dam was built. Archaeological findings there show humans lived there continuously from about 9,000 BCE until 1300 CE. Around 2200 BCE, people in the western Snake River area began to live in more settled ways, relying more on fish, especially salmon, and using methods to store food. Shoshone-speaking groups arrived in the Snake River Plain between 600 and 1500 CE.
By the time Europeans first arrived, the Snake River area was home to several Native American tribes. The Nez Perce (Nimiipuu) lived in what is now north-central Idaho, southeast Washington, and northeast Oregon, including much of the lower Snake River, the Clearwater and Grande Ronde Rivers, and the lower Salmon River. The Northern Shoshone and the Bannock, a group related to the Northern Paiute, lived in areas stretching from the Snake River Plain to the Rocky Mountains and the Great Basin, as well as the upper Salmon River. The Nez Perce called the Snake River Kimooenim or similar names, meaning "the stream/place of the hemp weed." Another name was Pikúunen, referring to the part of the river above the Clearwater River. The Wanapum and Walla Walla people called the lower Snake River below the Clearwater Naxíyam Wána. The Shoshone called the river Yampapah, after the yampah plant that grew along its banks.
Below Shoshone Falls, salmon and steelhead trout—fish that live in the ocean as adults but return to rivers to reproduce—were a major food source for Native peoples and held cultural importance. Ceremonies like the first salmon ceremony were common along rivers like the Columbia and Snake, and strict fishing rules helped ensure enough salmon survived to return to their birthplaces. The Nez Perce had more than seventy permanent villages near fishing areas on the Snake, Clearwater, and Salmon Rivers. Clans gathered at fishing spots starting in May or June. As summer progressed, fishing moved to higher streams, and fall salmon were stored for winter use.
Shoshone people in the western Snake River area also relied heavily on salmon. At Shoshone Falls and nearby waterfalls, large-scale fishing tools like platforms, weirs, spears, baskets, and traps were used. In 1832, Captain Benjamin Bonneville observed that "Indians at Salmon Falls on the Snake River took several thousand salmon in one afternoon by means of spears." To the east of the falls, many Shoshone and Bannock lived in nomadic groups, traveling to the falls during the spring salmon run, then gathering camas bulbs and hunting bison in the summer and autumn.
The Snake River at Hells Canyon was a natural boundary between the Nez Perce and Shoshone, who were enemies. The Nez Perce allied with the Cayuse to stop the Shoshone, Bannock, and Northern Paiute from expanding toward the Columbia Plateau. Both groups acquired horses in the late 1600s or early 1700s, which helped them trade and hunt over long distances. With horses, the Nez Perce could travel east of the Bitterroot Mountains to hunt bison, following the trail over Lolo Pass, which the Lewis and Clark expedition later used to reach the Snake and Columbia Rivers.
The river’s modern name comes from a misunderstanding of a Shoshone sign. Plains Indians called the Shoshone "Snake People," while the Shoshone may have called themselves "People of the River of Many Fish." However, the Shoshone sign for "salmon" was similar to the Plains Indian sign for "snake." The English name "Snake River" likely came from this confusion, though it is unclear when the name was first used.
The first Europeans to reach the Snake River area were the Lewis and Clark Expedition in 1805. They crossed the Continental Divide at Lemhi Pass and descended to the Salmon River, naming it "Lewis's River." Unable to navigate the river’s rapids, they crossed the Bitterroot Mountains via the Nez Perce trail at Lolo Pass. After traveling down the Clearwater River, they met the Nez Perce at the Snake River’s junction with the Columbia on October 10, 1805. They correctly identified the river from the south as a continuation of "Lewis's" or Salmon River. The Nez Perce called it Kimooenim, but William Clark later changed the name to "Lewis's." Six days later, they reached the confluence of the Snake and Columbia Rivers, noting dangerous rapids and many native fishing sites. The expedition formed friendly relations with the Nez Perce, who they visited again on their return trip in 1806.
Other explorers soon followed, including fur trappers searching for beaver. John Colter, a former member of the Lewis and Clark Expedition, explored Jackson Hole in 1808. In 1810, Andrew Henry explored and named the Henrys Fork of the Snake River, building Fort Henry—the first American fur trading post west of the Rocky Mountains—but abandoned it after a harsh winter. In 1811, Wilson Price Hunt led an expedition to find a route from Henrys Fork to the Columbia River. After a wreck at the Snake River Canyon, they took an overland route through the Snake River Plain, the Boise Valley, and the Blue Mountains to avoid Hells Canyon. Hunt later called the river "Mad River" due to the journey’s dangers. A group led by Robert Stuart mapped the route, which would later become part of the Oregon Trail.
In 1818, Donald Mackenzie and Alexander Ross established Fort Nez Percés for the North West Company near the Snake and Columbia Rivers’ confluence. The following year, Mackenzie traveled up the Snake River to Boise Valley, making the first recorded river ascent of Hells Canyon. His goal was to avoid the difficult trek over the Blue Mountains. He wrote that "the passage by water is now proved to be safe and practicable for loaded boats, without one single carrying place or portage." However, he noted that the river’s strong current and rapids might still make land travel preferable.
In 1819, Canadian fur trappers from the British Hudson’s Bay Company (HBC) reached the Snake River area. As American trappers arrived, the HBC ordered the Canadians to kill as many beavers as possible, believing that "if there are no beavers, there will be no reason for the Yanks to come." Even if Americans gained control, the HBC aimed to claim all the profits first. The HBC focused on the upper Snake River region, carrying out the "fur desert" policy in nine expeditions from about 1824–18.
Reclamation and development
Most travelers on the Oregon Trail saw the dry Snake River Plain as a challenge to cross, not a place to live. This changed when gold was found near Boise. The need for supplies for miners led to more farming in the Boise Valley. By the 1880s, settlers moved to the upper Snake River near Idaho Falls, where rich, sandy soil was perfect for growing Idaho potatoes. The dry climate required irrigation, so many private companies built canals. These systems worked well at first, but soon all the easy-to-farm land was used up. Companies could not afford to expand or build dams to store water during dry seasons.
Because many irrigation companies were near bankruptcy, the federal government started helping farmers. The 1894 Carey Act gave western states large areas of dry land to sell to farmers and investors. Investors could earn money by selling water rights to farmers. Engineers checked if projects were economically possible. While the Carey Act had little success elsewhere, Idaho benefited greatly. About 60% of land developed under the act was in Idaho, and most used water from the Snake River.
I.B. Perrine, who lived near Shoshone Falls in the 1880s, created one of the most successful Carey Act projects. In 1900, Perrine claimed water from the Snake River and used private money to build Milner Dam and a canal system. The project, completed in 1905, irrigated 250,000 acres of the Snake River Plain. This turned the area into productive farmland, leading to the nickname "Magic Valley" and the growth of Twin Falls. At times, nearly all the Snake River’s water was diverted through Milner Dam, causing Shoshone Falls to dry up in summer. The Idaho State Historical Society notes that Perrine’s project was a rare success compared to failed private irrigation efforts, showing the importance of federal support for farming.
In 1902, the federal government created the Reclamation Service (now the Bureau of Reclamation) to manage water resources. The Minidoka Project was the first major federal project in Idaho. Starting with Minidoka Dam in 1906, the project expanded to include reservoirs at Jackson Lake, American Falls, and Island Park, along with canals and pumps. It eventually brought water to a million acres in the Magic Valley. During World War II, Japanese Americans interned at Minidoka worked on the project. The Boise Project, which irrigated 500,000 acres around Boise, was another early success. Arrowrock Dam, completed in 1915, was the world’s tallest dam at the time and influenced future projects like the Hoover Dam.
Starting in the 1950s, farmers used water from the Snake River aquifer to grow crops. More surface water projects, like Cascade Dam (1948) and Anderson Ranch Dam (1950), helped the Boise Project. Palisades Dam (1956) provided flood control and irrigation above Idaho Falls, an area previously ignored. Teton Dam, built near Rexburg, failed in 1976, killing 11 people and causing over $400 million in damage. This disaster stopped large new irrigation projects for the Snake River and the Bureau of Reclamation.
Agriculture has affected water quality in the Snake River above Hells Canyon. Irrigation water becomes polluted with chemicals and manure, soaking into the Snake River Aquifer. Pollutants in groundwater eventually flow back into the river, causing excess nitrogen, phosphorus, and bacteria. Algae blooms often occur in summer. The U.S. Environmental Protection Agency has set rules for water quality in the Snake River, covering bacteria, mercury, nutrients, pesticides, sediments, and temperature. These rules include farming practices and regular water testing.
Power generation on the Snake River began in the early 1900s as cities, farms, and industries grew. The first hydroelectric plant, Swan Falls Dam, was built in 1901, followed by American Falls Dam in 1902. After developing Milner Dam, I.B. Perrine built a power plant at Shoshone Falls in 1907. Other plants were built at Salmon Falls (1910) and Thousand Springs (1912). Idaho Power, formed in 1915, bought these plants and built larger ones, including a second plant at Shoshone Falls in 1921 and another at Twin Falls in 1935. Electric pumps allowed farming in areas where water could not flow by gravity. The Minidoka Project used this system, selling extra power to nearby towns.
By the 1940s, interest in the Snake River’s power potential grew after large dams were built on the Columbia River. Idaho Power planned three dams in Hells Canyon, but the U.S. Army Corps of Engineers proposed a single, massive dam in lower Hells Canyon. In 1955, the Federal Power Commission approved Idaho Power’s plan, but only one dam, Brownlee (completed 1958), was built. Other proposals faced competition and flood risks. The Pacific Northwest Power Company planned the "High Mountain Sheep Dam" near the Salmon River, while the Washington Public Power Supply System proposed the "Nez Perce Dam" downstream. These projects faced challenges but highlighted the Snake River’s energy potential.
Ecology and environmental issues
The World Wide Fund for Nature (WWF) divides the Snake River into two freshwater ecoregions: the Upper Snake and the Columbia Unglaciated. Shoshone Falls marks the boundary between these two regions. Shoshone Falls has blocked fish from moving upstream since the Bonneville flood 15,000 years ago. The Big Wood River, which is the main branch of the Malad River, is also part of the Upper Snake ecoregion because of a natural waterfall that acts as a barrier. Because of these barriers, only 35% of the fish species above Shoshone Falls and 40% of the fish species in the Big Wood River are shared with the lower Snake River.
Compared to the lower Snake River and other parts of the Columbia River system, the Upper Snake ecoregion has many species that are found only in that area, especially freshwater snails and clams. At least 21 snail and clam species are in danger of disappearing, with 15 of them found only in small groups. There are 14 fish species that live only in the Upper Snake region and not elsewhere in the Columbia River watershed, but some of these also live in western Utah and the Yellowstone River. These include Yellowstone cutthroat trout and Snake River fine-spotted cutthroat trout. The Wood River sculpin is found only in the Wood River, and the Shoshone sculpin is found only in the part of the Snake River between Shoshone Falls and the Wood River.
The Snake River below Shoshone Falls is home to about 35 native fish species. Of these, 12 are also found in the Columbia River, and 4 are found only in the Snake River or nearby areas. These include the sand roller, shorthead sculpin, margined sculpin, and the Oregon chub, which also lives in some Oregon streams. Bull trout swim from the main Snake River to spawn in tributaries like the Bruneau, Imnaha, and Grande Ronde Rivers. Large white sturgeon, introduced to the Snake River in the 19th century, were once common below Shoshone Falls, but dam construction has left only a few small groups of sturgeon. The Idaho Department of Fish and Game has recorded sturgeon more than 10 feet long in Hells Canyon. Other introduced species include whitefish, pikeminnow, smallmouth bass, and rainbow, brown, brook, and lake trout.
Anadromous salmonids (a group of fish that migrate from the ocean to rivers to spawn), including chinook, coho, and sockeye salmon, and redband and steelhead trout, were once the most common fish in the Snake River and played a key role in the ecosystem. Before the 19th century, between 2 and 6 million adult salmon and steelhead returned each year from the Pacific to spawn in the Snake River. After spawning, these fish die, and their bodies provide important nutrients to rivers that lack other natural sources of food. The Salmon River, below Hells Canyon, had the richest spawning grounds, though many fish also reached areas above Hells Canyon, such as near Shoshone Falls. The Snake River produced about 40% of all chinook salmon and 50% of all steelhead in the Columbia River watershed.
Fish populations began to decrease in the late 1800s due to commercial fishing, logging, mining, and agriculture. Even in the 1930s, more than 500,000 fall chinook salmon returned to spawn. Populations dropped further after dams were built on the lower Snake and Columbia Rivers, and the Hells Canyon Dam blocked access to the upper Snake River. Wild chinook salmon and steelhead numbers fell from 130,000 in the 1950s to less than 5,000 in the 1990s. Both chinook and steelhead were listed as threatened in 1992 and 1997, respectively.
Wild chinook and steelhead populations continued to decline through the 1990s but began to recover slightly after 2000, with returns reaching 20,000–30,000 in some years. Coho salmon disappeared from the Snake River by the 1980s but were reintroduced in 1995.
Snake River sockeye salmon once numbered up to 150,000 adults. Between 24,000 and 30,000 sockeye returned to Wallowa Lake in the Grande Ronde River watershed, but the run ended by 1905 due to overharvesting and irrigation. The Payette Lake population was blocked by the Black Canyon Dam in 1924. Sockeye in the Yellowbelly, Stanley, and Pettit Lakes of the Sawtooth basin were eliminated by management actions in the 1950s, and irrigation caused the Pettit Lake population to disappear. Sockeye returns dropped to 4,500 in the 1950s and fewer than a few dozen by the late 1960s. Snake River sockeye were listed as endangered in 1991.
Many hatcheries, operated by groups like the Army Corps of Engineers, Idaho Power, and the U.S. Fish and Wildlife Service, release about 33 million salmon and steelhead smolt into the Snake River each year to support wild populations. However, few hatchery fish survive. Only 0.4% of hatchery chinook and 1.5% of hatchery steelhead return as adults, based on measurements at Lower Granite Dam between 2007 and 2016.
Upstream of the four lower dams, the Snake River has some of the best remaining spawning habitat in the Columbia River system, especially along the Clearwater and Salmon Rivers. The Salmon River is one of the longest undammed rivers in the United States. A small group of sockeye salmon still spawn in Redfish Lake near Stanley, Idaho, more than 900 miles from the Pacific Ocean. This is the southernmost, highest elevation, and longest sockeye salmon run in the world.
The Snake River provides important habitat for wildlife, especially in the dry Snake River Plain, where it is the only water source for many miles. The