Willamette River

The Willamette River (i/wɨˈlæmɨt/) is a major tributary of the Columbia River, accounting for 12 to 15 percent of the Columbia's flow. The Willamette's main stem is 187 miles (301 km) long, lying entirely in northwestern Oregon in the United States. Flowing northward between the Oregon Coast Range and the Cascade Range, the river and its tributaries form the Willamette Valley, a basin that contains two-thirds of Oregon's population, including the state capital, Salem, and the state's largest city, Portland. Portland surrounds the Willamette's mouth at the Columbia.

Originally created by plate tectonics about 35 million years ago and subsequently altered by volcanism and erosion, the river's drainage basin was significantly modified by the Missoula Floods at the end of the most recent ice age. Humans began living in the watershed over 10,000 years ago. There were once many tribal villages along the lower river and in the area around its mouth on the Columbia. Indigenous peoples lived throughout the upper reaches of the basin as well.

Rich with sediments deposited by flooding and fed by prolific rainfall on the western side of the Cascades, the Willamette Valley is one of the most fertile agricultural regions in North America, and was thus the destination of many 19th-century pioneers traveling west along the Oregon Trail. The river was an important transportation route during this time, although Willamette Falls, just upstream from Portland, was a major barrier to boat traffic. In the 21st century, major highways follow the river and roads cross it on more than 50 bridges.

Since 1900, more than 15 large dams and many smaller ones have been built in the Willamette's drainage basin, and 13 of them are managed by the U.S. Army Corps of Engineers (USACE). The dams are used primarily to produce hydroelectricity, to store water for irrigation, and to divert water into deeper, narrower channels in order to prevent flooding. The river and its tributaries support 60 fish species, including many species of salmon and trout; this is despite the dams, other alterations, and pollution (especially on the river's lower reaches). Part of the Willamette Floodplain was established as a National Natural Landmark in 1987 and the river was named as one of 14 American Heritage Rivers in 1998.

Read more about Willamette River:  Course, Geology, Watershed, Flooding, Pollution, Flora and Fauna

Other articles related to "willamette river, willamette, river":

Steamboats Of The Columbia River - Areas of Operation - Willamette River
... The Willamette River flows northwards down the Willamette Valley until it meets the Columbia River at a point 101 miles (163 km) from the mouth of the Columbia ... In the natural condition of the river, Portland was the farthest point on the river where the water was deep enough to allow ocean-going ships ... Rapids further upstream at Clackamas were a hazard to navigation, and all river traffic had to portage around Willamette Falls, where Oregon City had been ...
Middle Fork Willamette River
... The Middle Fork Willamette River is one of several forks that unite to form the Willamette River in the western part of the U.S. 115 mi (185 km) long, draining an area of the mountains at the south end of the Willamette Valley south of Eugene ...
Steamboats Of The Willamette River - Operations On Willamette River
... The Willamette River was readily navigable by steamboats all the way up to Milwaukie ... Above Milwaukie, there were two barriers to navigation, the Clackamas Rapids and Willamette Falls ... Willamette Falls was impassable ...
Willamette River - Flora and Fauna
... Over the past 150 years, a significant change for the Willamette River has been the loss of its floodplain forests, which covered an estimated 89 percent of a 400-foot (120 m) band ... The remaining forests close to the river include large stands of black cottonwood, Oregon ash, willow, and bigleaf maple ... Fish in the Willamette basin include 31 native species, among them cutthroat, bull, and rainbow trout, several species of salmon, sucker, minnow, sculpin, and lamprey, as well as sturgeon, stickleback, and others ...
Columbia Slough - Course
1.7 miles (0.6 to 2.7 km) south of the Columbia River in Multnomah County ... westward for about another 18 miles (29 km) to its confluence with the Willamette River ... At about river mile (RM) 15.5 or river kilometer (RK) 24.9, it passes through a gated levee that separates the upper slough from the middle slough ...

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