Columbia River

Course

The Columbia begins its 1,243-mile (2,000 km) journey in the southern Rocky Mountain Trench in British Columbia (BC). Columbia Lake – 2,690 ft (820 m) above sea level – and the adjoining Columbia Wetlands form the river's headwaters. The trench is a broad, deep, and long glacial valley between the Canadian Rockies and the Columbia Mountains in BC. For its first 200 mi (320 km), the Columbia flows northwest along the trench through Windermere Lake and the town of Invermere, a region known in BC as the Columbia Valley, then northwest to Golden and into Kinbasket Lake. Rounding the northern end of the Selkirk Mountains, the river turns sharply south through a region known as the Big Bend Country, passing through Revelstoke Lake and the Arrow Lakes. Revelstoke, the Big Bend, and the Columbia Valley are collectively referred to in BC parlance as the Columbia Country. Below the Arrow Lakes, the Columbia passes the cities of Castlegar, located at the Columbia's confluence with the Kootenay River, and Trail, two major population centers of the West Kootenay region. The Pend Oreille River joins the Columbia about 0.2 miles (0.3 km) north of the Canada–United States border.

The Columbia enters eastern Washington flowing south and turning to the west at the Spokane River confluence. It marks the southern and eastern borders of the Colville Indian Reservation and the western border of the Spokane Indian Reservation. The river turns south after the Okanogan River confluence, then southeasterly near the confluence with the Wenatchee River in central Washington. This C-shaped segment of the river is also known as the "Big Bend". During the Missoula Floods 10–15,000 years ago, much of the floodwater took a more direct route south, forming the ancient river bed known as the Grand Coulee. After the floods, the river found its present course, and the Grand Coulee was left dry. The construction of the Grand Coulee Dam in the mid-20th century impounded the river, forming Lake Roosevelt, from which water was pumped into the dry coulee, forming the reservoir of Banks Lake.

The river flows past The Gorge Amphitheatre, a prominent concert venue in the Northwest, then through Priest Rapids Dam, and then through the Hanford Nuclear Reservation. Entirely within the reservation is Hanford Reach, the only U.S. stretch of the river that is completely free-flowing, unimpeded by dams, and not a tidal estuary. The Snake River and Yakima River join the Columbia in the Tri-Cities population center. The Columbia makes a sharp bend to the west at the Washington–Oregon border. The river defines that border for the final 309 mi (497 km) of its journey.

Discharge

With an average flow at the mouth of about 265,000 cu ft/s (7,500 m3/s), the Columbia is the largest river by discharge flowing into the Pacific from the Americas and is the fourth-largest by volume in the U.S. The average flow where the river crosses the international border between Canada and the United States is 2,790 m3/s (99,000 cu ft/s) from a drainage basin of 102,800 km2 (39,700 mi2). This amounts to about 15 percent of the entire Columbia watershed. The Columbia's highest recorded flow, measured at The Dalles, was 1,240,000 cu ft/s (35,000 m3/s) in June 1894, before the river was dammed. The lowest flow recorded at The Dalles was 12,100 cu ft/s (340 m3/s) on April 16, 1968, and was caused by the initial closure of the John Day Dam, 28 mi (45 km) upstream. The Dalles is about 190 mi (310 km) from the mouth; the river at this point drains about 237,000 mi2 (610,000 km2) or about 91 percent of the total watershed. Flow rates on the Columbia are affected by many large upstream reservoirs, many diversions for irrigation, and, on the lower stretches, reverse flow from the tides of the Pacific Ocean. The National Ocean Service observes water levels at six tide gauges and issues tide forecasts for twenty-two additional locations along the river between the entrance at the North Jetty and the base of Bonneville Dam, its head of tide.

*1858–1899: 6,280 m3/s

Geology

When the rifting of Pangaea, due to the process of plate tectonics, pushed North America away from Europe and Africa and into the Panthalassic Ocean (ancestor to the modern Pacific Ocean), the Pacific Northwest was not part of the continent. As the North American continent moved westward, the Farallon Plate subducted under its western margin. As the plate subducted, it carried along island arcs which were accreted to the North American continent, resulting in the creation of the Pacific Northwest between 150 and 90 million years ago. The general outline of the Columbia Basin was not complete until between 60 and 40 million years ago, but it lay under a large inland sea later subject to uplift. Between 50 and 20 million years ago, from the Eocene through the Miocene eras, tremendous volcanic eruptions frequently modified much of the landscape traversed by the Columbia. The lower reaches of the ancestral river passed through a valley near where Mount Hood later arose. Carrying sediments from erosion and erupting volcanoes, it built a 2-mile (3.2 km) thick delta that underlies the foothills on the east side of the Coast Range near Vernonia in northwestern Oregon. Between 17 million and 6 million years ago, huge outpourings of flood basalt lava covered the Columbia Plateau and forced the lower Columbia into its present course. The modern Cascade Range began to uplift 5 to 4 million years ago. Cutting through the uplifting mountains, the Columbia River significantly deepened the Columbia River Gorge.

The river and its drainage basin experienced some of the world's greatest known catastrophic floods toward the end of the last ice age. The periodic rupturing of ice dams at Glacial Lake Missoula resulted in the Missoula Floods, with discharges exceeding the combined flow of all the other rivers in the world, dozens of times over thousands of years. While the exact number of floods is unknown, geologists have documented at least 40; evidence suggests that they occurred between about 19,000 and 13,000 years ago.

The floodwaters rushed across eastern Washington, creating the channeled scablands, which are a complex network of dry canyon-like channels, or coulees that are often braided and sharply gouged into the basalt rock underlying the region's deep topsoil. Numerous flat-topped buttes with rich soil stand high above the chaotic scablands. Constrictions at several places caused the floodwaters to pool into large temporary lakes, such as Lake Lewis, in which sediments were deposited. Water depths have been estimated at 1,000 feet (300 m) at Wallula Gap and 400 feet (120 m) over modern Portland, Oregon. Sediments were also deposited when the floodwaters slowed in the broad flats of the Quincy, Othello, and Pasco Basins. The floods' periodic inundation of the lower Columbia Plateau deposited rich sediments; 21st-century farmers in the Willamette Valley "plow fields of fertile Montana soil and clays from Washington's Palouse".

Indigenous peoples

Humans have inhabited the Columbia's watershed for more than 15,000 years, with a transition to a sedentary lifestyle based mainly on salmon starting about 3,500 years ago. In 1962, archaeologists found evidence of human activity dating back 11,230 years at the Marmes Rockshelter, near the confluence of the Palouse and Snake rivers in eastern Washington. In 1996 the skeletal remains of a 9,000-year-old prehistoric man (dubbed Kennewick Man) were found near Kennewick, Washington. The discovery rekindled debate in the scientific community over the origins of human habitation in North America and sparked a protracted controversy over whether the scientific or Native American community was entitled to possess and/or study the remains.

Many different Native Americans and First Nations peoples have a historical and continuing presence on the Columbia. South of the Canada–US border, the Colville, Spokane, Coeur d'Alene, Yakama, Wanapum, Nez Perce, Cayuse, Palus, Umatilla, Cowlitz, and the Confederated Tribes of Warm Springs live along the US stretch. Along the upper Snake River and Salmon River, the Shoshone Bannock tribes are present. The Sinixt or Lakes people lived on the lower stretch of the Canadian portion, while above that the Shuswap people (Secwepemc in their own language) reckon the whole of the upper Columbia east to the Rockies as part of their territory. The Canadian portion of the Columbia Basin outlines the traditional homelands of the Canadian Kootenay–Ktunaxa.

The Chinook tribe, which is not federally recognized, who live near the lower Columbia River, call it Wimahl or Wimal in the Upper Chinook (Kiksht) language, and it is Nch’i-Wàna or Nchi wana to the Sahaptin (Ichishkíin Sɨ́nwit)-speaking peoples of its middle course in present-day Washington. The river is known as swah'netk'qhu by the Sinixt people, who live in the area of the Arrow Lakes in the river's upper reaches in Canada. All three terms essentially mean "the big river".

Oral histories describe the formation and destruction of the Bridge of the Gods, a land bridge that connected the Oregon and Washington sides of the river in the Columbia River Gorge. The bridge, which aligns with geological records of the Bonneville Slide, was described in some stories as the result of a battle between gods, represented by Mount Adams and Mount Hood, in their competition for the affection of a goddess, represented by Mount St. Helens. Native American stories about the bridge differ in their details but agree in general that the bridge permitted increased interaction between tribes on the north and south sides of the river.

New waves of explorers

Historian Derek Hayes believes that Japanese or Chinese vessels blown off course reached the Northwest Coast long before Europeans—possibly as early as 219 BCE—but the earliest known wreck is from the 19th century.

The Maris Pacifici map published in 1589 features on the west coast of North-America an intriguing resemblance of two major coastline features: the mouth of the Columbia River identified as "Rio Grande" and the delta of the Fraser River labeled "Baia de las isleas". These rivers may have been sighted by European visitors long before official records would confirm nearly 200 years later. In spite of limited evidence of Francis Drake expedition 1579 whereabouts in the Pacific Northwest, Pacific Northwest BC history commentator Sam Bawlf posited that the Ortelius mapped coastal features were a proof that Drake sighted the mouth of the Columbia and the Fraser River delta. The Beeswax wreck proves that Spanish vessels reached the shore by the late-17th century, but if there were any survivors, they failed to send word home to Spain.

In the 18th century, there was strong interest in discovering a Northwest Passage that would permit navigation between the Atlantic (or inland North America) and the Pacific oceans. Many ships in the area, especially those under Spanish and British command, searched the northwest coast for a large river that might connect to Hudson Bay or the Missouri River. The first documented European discovery of the Columbia River was that of Bruno de Heceta, who in 1775 sighted the river's mouth. On the advice of his officers, he did not explore it, as he was short-staffed and the current was strong. He considered it a bay, and called it Ensenada de Asunción (Assumption Cove). Later Spanish maps, based on his sighting, showed a river, labeled Río de San Roque (The Saint Roch River), or an entrance, called Entrada de Hezeta, named for Bruno de Hezeta, who sailed the region. Following Hezeta's reports, British maritime fur trader Captain John Meares searched for the river in 1788 but concluded that it did not exist. He named Cape Disappointment for the non-existent river, not realizing the cape marks the northern edge of the river's mouth.

What happened next would form the basis for decades of both cooperation and dispute between British and American exploration of, and ownership claim to, the region. Royal Navy commander George Vancouver sailed past the mouth in April 1792 and observed a change in the water's color, but he accepted Meares' report and continued on his journey northward. Later that month, Vancouver encountered the American captain Robert Gray at the Strait of Juan de Fuca. Gray reported that he had seen the entrance to the Columbia and had spent nine days trying but failing to enter.

Navigation

American captain Robert Gray and British captain George Vancouver, who explored the river in 1792, proved that it was possible to cross the Columbia Bar. Many of the challenges associated with that feat remain today; even with modern engineering alterations to the mouth of the river, the strong currents and shifting sandbar make it dangerous to pass between the river and the Pacific Ocean.

The use of steamboats along the river, beginning with the British Beaver in 1836 and followed by American vessels in 1850, contributed to the rapid settlement and economic development of the region. Steamboats operated in several distinct stretches of the river: on its lower reaches, from the Pacific Ocean to Cascades Rapids; from the Cascades to The Dalles-Celilo Falls; from Celilo to the Priest Rapids; on the Wenatchee Reach of eastern Washington; on British Columbia's Arrow Lakes; and on tributaries like the Willamette, the Snake and Kootenay Lake. The boats, initially powered by burning wood, carried passengers and freight throughout the region for many years. Early railroads served to connect steamboat lines interrupted by waterfalls on the river's lower reaches. In the 1880s, railroads maintained by companies such as the Oregon Railroad and Navigation Company began to supplement steamboat operations as the major transportation links along the river.

Opening the passage to Lewiston

As early as 1881, industrialists proposed altering the natural channel of the Columbia to improve navigation. Changes to the river over the years have included the construction of jetties at the river's mouth, dredging, and the construction of canals and navigation locks. Today, ocean freighters can travel upriver as far as Portland and Vancouver, and barges can reach as far inland as Lewiston, Idaho.

The shifting Columbia Bar makes passage between the river and the Pacific Ocean difficult and dangerous, and numerous rapids along the river hinder navigation. Pacific Graveyard, a 1950 book by James A. Gibbs, describes the many shipwrecks near the mouth of the Columbia. Jetties, first constructed in 1886, extend the river's channel into the ocean. Strong currents and the shifting sandbar remain a threat to ships entering the river and necessitate continuous maintenance of the jetties.

In 1891, the Columbia was dredged to enhance shipping. The channel between the ocean and Portland and Vancouver was deepened from 17 to 25 feet (5.2 to 7.6 m). The Columbian called for the channel to be deepened to 40 feet (12 m) as early as 1905, but that depth was not attained until 1976.

Cascade Locks and Canal were first constructed in 1896 around the Cascades Rapids, enabling boats to travel safely through the Columbia River Gorge. The Celilo Canal, bypassing Celilo Falls, opened to river traffic in 1915. In the mid-20th century, the construction of dams along the length of the river submerged the rapids beneath a series of reservoirs. An extensive system of locks allowed ships and barges to pass easily between reservoirs. A navigation channel reaching Lewiston, Idaho, along the Columbia and Snake rivers, was completed in 1975. Among the main commodities are wheat and other grains, mainly for export. As of 2016, the Columbia ranked third, behind the Mississippi and Paraná rivers, among the world's largest export corridors for grain.

The 1980 eruption of Mount St. Helens caused mudslides in the area, which reduced the Columbia's depth by 25 feet (7.6 m) for a 4-mile (6.4 km) stretch, disrupting Portland's economy.

Deeper shipping channel

Efforts to maintain and improve the navigation channel have continued to the present day. In 1990 a new round of studies examined the possibility of further dredging on the lower Columbia. The plans were controversial from the start because of economic and environmental concerns.

In 1999, Congress authorized deepening the channel between Portland and Astoria from 40 to 43 feet (12–13 m), which will make it possible for large container and grain ships to reach Portland and Vancouver. The project has met opposition because of concerns about stirring up toxic sediment on the riverbed. Portland-based Northwest Environmental Advocates brought a lawsuit against the Army Corps of Engineers, but it was rejected by the Ninth U.S. Circuit Court of Appeals in August 2006. The project includes measures to mitigate environmental damage; for instance, the US Army Corps of Engineers must restore 12 times the area of wetland damaged by the project. In early 2006, the Corps spilled 50 US gallons (190 L) of hydraulic oil into the Columbia, drawing further criticism from environmental organizations.

Work on the project began in 2005 and concluded in 2010. The project's cost is estimated at $150 million. The federal government is paying 65 percent, Oregon and Washington are paying $27 million each, and six local ports are also contributing to the cost.

The lower Columbia River, the Snake River as far as Lewiston, and part of the Willamette River make up M-84, a route of the United States Marine Highway Program.

Dams

In 1902, the United States Bureau of Reclamation was established to aid in the economic development of arid western states. One of its major undertakings was building Grand Coulee Dam to provide irrigation for the 600 thousand acres (2,400 km2) of the Columbia Basin Project in central Washington. With the onset of World War II, the focus of dam construction shifted to production of hydroelectricity. Irrigation efforts resumed after the war.

River development occurred within the structure of the 1909 International Boundary Waters Treaty between the United States and Canada. The United States Congress passed the Rivers and Harbors Act of 1925, which directed the U.S. Army Corps of Engineers and the Federal Power Commission to explore the development of the nation's rivers. This prompted agencies to conduct the first formal financial analysis of hydroelectric development; the reports produced by various agencies were presented in House Document 308. Those reports, and subsequent related reports, are referred to as 308 Reports.

The 308 Reports generated 176 publications across the United States. Of those 176 documents, thirteen of them were generated in the Pacific Northwest. In 1932, one of the thirteen reports was released on the Columbia River, titled The Columbia River and Minor Tributaries. The report was backed by many engineers and state politicians who believed that the creation of dams along the Columbia River would be a strong candidate for generation of hydroelectric power. The report led to congressional action, where dams at Bonneville and Grand Coulee were authorized in 1933.

The report itself emphasized the economic values of dam creation. Additionally, the reports emphasized the importance of dams for river navigation. Furthermore, the reports emphasized the importance of hydropower, storage of water for irrigation techniques, and flood control. To ensure that the dams did not affect biodiversity, many engineers and state politicians regarded the importance of salmon within the region. Thus, dams were to be built at a low height that would permit salmon to pass over.

In the late 1920s, political forces in the Northwestern United States generally favored the private development of hydroelectric dams along the Columbia. But the overwhelming victories of gubernatorial candidate George W. Joseph in the 1930 Republican primary, and later his law partner Julius Meier, were understood to demonstrate strong public support for public ownership of dams. In 1933, President Franklin D. Roosevelt signed a bill that enabled the construction of the Bonneville and Grand Coulee dams as public works projects. The legislation was attributed to the efforts of Oregon Senator Charles McNary, Washington Senator Clarence Dill, and Oregon Congressman Charles Martin, among others.

Irrigation

The Bureau of Reclamation's Columbia Basin Project focused on the generally dry region of central Washington known as the Columbia Basin, which features rich loess soil. Several groups developed competing proposals, and in 1933, President Franklin D. Roosevelt authorized the Columbia Basin Project. The Grand Coulee Dam was the project's central component; upon completion, it pumped water up from the Columbia to fill the formerly dry Grand Coulee, forming Banks Lake. By 1935, the intended height of the dam was increased from a range between 200 and 300 feet (61 and 91 m) to 500 feet (150 m), a height that would extend the lake impounded by the dam to the Canada–United States border; the project had grown from a local New Deal relief measure to a major national project.

The project's initial purpose was irrigation, but the onset of World War II created a high electricity demand, mainly for aluminum production and for the development of nuclear weapons at the Hanford Site. Irrigation began in 1951. The project provides water to more than 670 thousand acres (2,700 square kilometers) of fertile but arid land in central Washington, transforming the region into a major agricultural center. Important crops include orchard fruit, potatoes, alfalfa, mint, beans, beets, and wine grapes.

Since 1750, the Columbia has experienced six multi-year droughts. The longest, lasting 12 years in the mid‑19th century, reduced the river's flow to 20 percent below average. Scientists have expressed concern that a similar drought would have grave consequences in a region so dependent on the Columbia. In 1992–1993, a lesser drought affected farmers, hydroelectric power producers, shippers, and wildlife managers.

Many farmers in central Washington build dams on their property for irrigation and to control frost on their crops. The Washington Department of Ecology, using new techniques involving aerial photographs, estimated there may be as many as a hundred such dams in the area, most of which are illegal. Six such dams have failed in recent years, causing hundreds of thousands of dollars of damage to crops and public roads. Fourteen farms in the area have gone through the permitting process to build such dams legally.

Hydroelectricity

The Columbia's heavy flow and large elevation drop over a short distance, 2.16 feet per mile (40.9 centimeters per kilometer), give it tremendous capacity for hydroelectricity generation. In comparison, the Mississippi drops less than 0.65 feet per mile (12.3 cm/km). The Columbia alone possesses one-third of the United States's hydroelectric potential. In 2012, the river and its tributaries accounted for 29 GW of hydroelectric generating capacity, contributing 44 percent of the total hydroelectric generation in the nation.

The largest of the 150 hydroelectric projects, the Grand Coulee Dam and Chief Joseph Dam are also the largest in the United States. As of 2017, Grand Coulee is the fifth largest hydroelectric plant in the world.

Inexpensive hydropower supported the location of a large aluminum industry in the region because its reduction from bauxite requires large amounts of electricity. Until 2000, the Northwestern United States produced up to 17 percent of the world's aluminum and 40 percent of the aluminum produced in the United States. The commoditization of power in the early 21st century, coupled with a drought that reduced the generation capacity of the river, damaged the industry and by 2001, Columbia River aluminum producers had idled 80 percent of its production capacity. By 2003, the entire United States produced only 15 percent of the world's aluminum and many smelters along the Columbia had gone dormant or out of business.

Power remains relatively inexpensive along the Columbia, and since the mid-2000 several global enterprises have moved server farm operations into the area to avail themselves of cheap power. Downriver of Grand Coulee, each dam's reservoir is closely regulated by the Bonneville Power Administration (BPA), the U.S. Army Corps of Engineers, and various Washington public utility districts to ensure flow, flood control, and power generation objectives are met. Increasingly, hydro-power operations are required to meet standards under the U.S. Endangered Species Act and other agreements to manage operations to minimize impacts on salmon and other fish, and some conservation and fishing groups support removing four dams on the lower Snake River, the largest tributary of the Columbia.

In 1941, the BPA hired Oklahoma folksinger Woody Guthrie to write songs for a documentary film promoting the benefits of hydropower. In the month he spent traveling the region Guthrie wrote 26 songs, which have become an important part of the cultural history of the region.

Ecology and environment

Fish migration

The Columbia supports several species of anadromous fish that migrate between the Pacific Ocean and freshwater tributaries of the river. Sockeye, Coho and Chinook ("king") salmon, and steelhead, all of the genus Oncorhynchus, are ocean fish that migrate up the rivers at the end of their life cycles to spawn. White sturgeon, which take 15 to 25 years to mature, typically migrate between the ocean and the upstream habitat several times during their lives.

Salmon populations declined dramatically after the establishment of canneries in 1867. In 1879 it was reported that 545,450 salmon, with an average weight of 22 pounds (10.0 kg) were caught (in a recent season) and mainly canned for export to England. A can weighing 1 pound (0.45 kg) could be sold for 8 or 9 pence. By 1908, there was widespread concern about the decline of salmon and sturgeon. In that year, the people of Oregon passed two laws under their newly instituted program of citizens' initiatives limiting fishing on the Columbia and other rivers. Then in 1948, another initiative banned the use of seine nets (devices already used by Native Americans, and refined by later settlers) altogether.

Dams interrupt the migration of anadromous fish. Salmon and steelhead return to the streams in which they were born to spawn; where dams prevent their return, entire populations of salmon die. Some of the Columbia and Snake River dams employ fish ladders, which are effective to varying degrees at allowing these fish to travel upstream. Another problem exists for the juvenile salmon headed downstream to the ocean. Previously, this journey would have taken two to three weeks. With river currents slowed by the dams, and the Columbia converted from a wild river to a series of slackwater pools, the journey can take several months, which increases the mortality rate. In some cases, the Army Corps of Engineers transports juvenile fish downstream by truck or river barge. The Chief Joseph Dam and several dams on the Columbia's tributaries entirely block migration, and there are no migrating fish on the river above these dams. Sturgeons have different migration habits and can survive without ever visiting the ocean. In many upstream areas cut off from the ocean by dams, sturgeon simply live upstream of the dam.

Not all fish have suffered from the modifications to the river; the northern pikeminnow (formerly known as the squawfish) thrives in the warmer, slower water created by the dams. Research in the mid-1980s found that juvenile salmon were suffering substantially from the predatory pikeminnow, and in 1990, in the interest of protecting salmon, a "bounty" program was established to reward anglers for catching pikeminnow.

Pollution

In southeastern Washington, a 50-mile (80 km) stretch of the river passes through the Hanford Site, established in 1943 as part of the Manhattan Project. The site served as a plutonium production complex, with nine nuclear reactors and related facilities along the banks of the river. From 1944 to 1971, pump systems drew cooling water from the river and, after treating this water for use by the reactors, returned it to the river. Before being released back into the river, the used water was held in retention basins for up to six hours. Longer-lived isotopes were not affected by this retention, and several terabecquerels entered the river every day. By 1957, the eight plutonium production reactors at Hanford dumped a daily average of 50,000 curies of radioactive material into the Columbia. These releases were kept secret by the federal government until the release of declassified documents in the late 1980s. Radiation was measured downstream as far west as the Washington and Oregon coasts.

The nuclear reactors were decommissioned at the end of the Cold War, and the Hanford site is the focus of one of the world's largest environmental cleanup, managed by the Department of Energy under the oversight of the Washington Department of Ecology and the Environmental Protection Agency. Nearby aquifers contain an estimated 270 billion US gallons (1 billion m3) of groundwater contaminated by high-level nuclear waste that has leaked out of Hanford's underground storage tanks. As of 2008, 1 million US gallons (3,785 m3) of highly radioactive waste is traveling through groundwater toward the Columbia River. This waste was expected to reach the river within 12 to 50 years if cleanup did not proceed on schedule.

In addition to concerns about nuclear waste, numerous other pollutants are found in the river. These include chemical pesticides, bacteria, arsenic, dioxins, and polychlorinated biphenyls (PCB).

Studies have also found significant levels of toxins in fish and the waters they inhabit within the basin. Accumulation of toxins in fish threatens the survival of fish species, and human consumption of these fish can lead to health problems. Water quality is also an important factor in the survival of other wildlife and plants that grow in the Columbia River drainage basin. The states, indigenous tribes, and federal government are all engaged in efforts to restore and improve the water, land, and air quality of the Columbia River drainage basin and have committed to work together to accomplish critical ecosystem restoration efforts. Several cleanup efforts are underway, including Superfund projects at Portland Harbor, Hanford, and Lake Roosevelt.

Nutrient cycle

Both natural and anthropogenic processes are involved in the cycling of nutrients in the Columbia River basin. Natural processes in the system include estuarine mixing of fresh and ocean waters, and climate variability patterns such as the Pacific Decadal Oscillation and the El Nino Southern Oscillation (both climatic cycles that affect the amount of regional snowpack and river discharge). Natural sources of nutrients in the Columbia River include weathering, leaf litter, salmon carcasses, runoff from its tributaries, and ocean estuary exchange. Major anthropogenic impacts on nutrients in the basin are due to fertilizers from agriculture, sewage systems, logging, and the construction of dams.

Nutrient dynamics vary in the river basin from the headwaters to the main river and dams, to finally reaching the Columbia River estuary and ocean. Upstream in the headwaters, salmon runs are the main source of nutrients. Dams along the river impact nutrient cycling by increasing residence time of nutrients, and reducing the transport of silicate to the estuary, which directly impacts diatoms, a type of phytoplankton. The dams are also a barrier to salmon migration and can increase the amount of methane locally produced. The Columbia River estuary exports high rates of nutrients into the Pacific, except for nitrogen, which is delivered into the estuary by ocean upwelling sources.

Watershed

Most of the Columbia's drainage basin (which, at 258,000 square miles or 670,000 square kilometres, is about the size of France) lies roughly between the Rocky Mountains on the east and the Cascade Mountains on the west. In the United States and Canada the term watershed is often used to mean drainage basin. The term Columbia Basin is used to refer not only to the entire drainage basin but also to subsets of the river's watershed, such as the relatively flat and unforested area in eastern Washington bounded by the Cascades, the Rocky Mountains, and the Blue Mountains. Within the watershed are diverse landforms including mountains, arid plateaus, river valleys, rolling uplands, and deep gorges. Grand Teton National Park lies in the watershed, as well as parts of Yellowstone National Park, Glacier National Park, Mount Rainier National Park, and North Cascades National Park. Canadian National Parks in the watershed include Kootenay National Park, Yoho National Park, Glacier National Park, and Mount Revelstoke National Park. Hells Canyon, the deepest gorge in North America, and the Columbia Gorge are in the watershed. Vegetation varies widely, ranging from western hemlock and western redcedar in the moist regions to sagebrush in the arid regions. The watershed provides habitat for 609 known fish and wildlife species, including the bull trout, bald eagle, gray wolf, grizzly bear, and Canada lynx.

The World Wide Fund for Nature (WWF) divides the waters of the Columbia and its tributaries into three freshwater ecoregions: Columbia Glaciated, Columbia Unglaciated, and Upper Snake. The Columbia Glaciated ecoregion, about a third of the total watershed, lies in the north and was covered with ice sheets during the Pleistocene. The ecoregion includes the mainstem Columbia north of the Snake River and tributaries such as the Yakima, Okanagan, Pend Oreille, Clark Fork, and Kootenay rivers. The effects of glaciation include a number of large lakes and a relatively low diversity of freshwater fish. The Upper Snake ecoregion is defined as the Snake River watershed above Shoshone Falls, which totally blocks fish migration. This region has 14 species of fish, many of which are endemic. The Columbia Unglaciated ecoregion makes up the rest of the watershed. It includes the mainstem Columbia below the Snake River and tributaries such as the Salmon, John Day, Deschutes, and lower Snake rivers. Of the three ecoregions it is the richest in terms of freshwater species diversity. There are 35 species of fish, of which four are endemic. There are also high levels of mollusk endemism.

In 2016, over eight million people lived within the Columbia's drainage basin. Of this total about 3.5 million people lived in Oregon, 2.1 million in Washington, 1.7 million in Idaho, half a million in British Columbia, and 0.4 million in Montana. Population in the watershed has been rising for many decades and is projected to rise to about 10 million by 2030. The highest population densities are found west of the Cascade Mountains along the I-5 corridor, especially in the Portland-Vancouver urban area. High densities are also found around Spokane, Washington, and Boise, Idaho. Although much of the watershed is rural and sparsely populated, areas with recreational and scenic values are growing rapidly. The central Oregon county of Deschutes is the fastest-growing in the state. Populations have also been growing just east of the Cascades in central Washington around the city of Yakima and the Tri-Cities area. Projections for the coming decades assume growth throughout the watershed. The Canadian part of the Okanagan subbasin is also growing rapidly.

Major tributaries

The Columbia receives more than 60 significant tributaries. The four largest that empty directly into the Columbia (measured either by discharge or by size of watershed) are the Snake River (mostly in Idaho), the Willamette River (in northwest Oregon), the Kootenay River (mostly in British Columbia), and the Pend Oreille River (mostly in northern Washington and Idaho, also known as the lower part of the Clark Fork). Each of these four averages more than 20,000 cubic feet per second (570 m3/s) and drains an area of more than 20,000 square miles (52,000 km2).

The Snake is by far the largest tributary. Its watershed of 108,000 square miles (280,000 km2) is larger than the state of Idaho. Its discharge is roughly a third of the Columbia's at the rivers' confluence but compared to the Columbia upstream of the confluence the Snake is longer (113%) and has a larger drainage basin (104%).

The Pend Oreille River system (including its main tributaries, the Clark Fork and Flathead rivers) is also similar in size to the Columbia at their confluence. Compared to the Columbia River above the two rivers' confluence, the Pend Oreille-Clark-Flathead is nearly as long (about 86%), its basin about three-fourths as large (76%), and its discharge over a third (37%).