<P> In the late 18th century, a private American ship became the first non-indigenous vessel to enter the river; it was followed by a British explorer, who navigated past the Oregon Coast Range into the Willamette Valley . In the following decades, fur trading companies used the Columbia as a key transportation route . Overland explorers entered the Willamette Valley through the scenic but treacherous Columbia River Gorge, and pioneers began to settle the valley in increasing numbers . Steamships along the river linked communities and facilitated trade; the arrival of railroads in the late 19th century, many running along the river, supplemented these links . </P> <P> Since the late 19th century, public and private sectors have heavily developed the river . To aid ship and barge navigation, locks have been built along the lower Columbia and its tributaries, and dredging has opened, maintained, and enlarged shipping channels . Since the early 20th century, dams have been built across the river for power generation, navigation, irrigation, and flood control . The 14 hydroelectric dams on the Columbia's main stem and many more on its tributaries produce more than 44 percent of total U.S. hydroelectric generation . Production of nuclear power has taken place at two sites along the river . Plutonium for nuclear weapons was produced for decades at the Hanford Site, which is now the most contaminated nuclear site in the US . These developments have greatly altered river environments in the watershed, mainly through industrial pollution and barriers to fish migration . </P> <P> 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 feet (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 miles (320 km), the Columbia flows northwest along the trench through Windermere Lake and the town of Invermere, a region known in British Columbia 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 combined are 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 2 miles (3 km) north of the US--Canada border . </P> <P> 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 10,000 to 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 . </P>

Where is the headwaters of the columbia river
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