The Columbia River (known as Wimahl or Big River to the Chinook-speaking natives who lived on its lowermost reaches) is the largest river in the Pacific Northwest region of North America. It is named after the Columbia Rediviva, the first ship from the western world known to have traveled up the river. It stretches from British Columbia through Washington state, forming much of the border between Washington and Oregon before emptying into the Pacific Ocean. The river is long, and its drainage basin is .

Measured by the volume of its flow, the Columbia is the largest river flowing into the Pacific from North America and is the fourth-largest river in the U.S. The river's heavy flow, and its large elevation drop over a relatively short distance, give it tremendous potential for the generation of electricity. It is the largest hydroelectric power producing river in North America with fourteen hydroelectric dams in the U.S. and Canada, and many more on various tributaries.

The Columbia and its tributaries are home to numerous anadromous fish, which migrate between fresh water streams and the Pacific Ocean. These fish—especially the various species of salmon—have been a vital part of the river's ecology and the local economy for thousands of years.

The Columbia has been heavily developed to serve human purposes since the arrival of numerous American and European settlers in the 19th century. The development, commonly referred to as taming or harnessing of the river, includes dredging for navigation by larger ships; the construction of dams for power generation, irrigation, navigation, and flood control; nuclear weapons research and production; and the generation of nuclear power. These projects have come into conflict with ecological conservation numerous times, impacting fish migration and resulting in industrial pollution.

Course

The Columbia flows from its headwaters in British Columbia (BC), Canada, to the Pacific Ocean on the Oregon–Washington border in the United States. It drains an area of about , including the discharge of its numerous tributaries. Its drainage basin covers nearly all of Idaho, large portions of BC, Oregon, and Washington, and small portions of Montana, Wyoming, Utah, and Nevada. Roughly of the river's length and 85 percent of its drainage basin are in the U.S. The Columbia is the twelfth-longest river and has the sixth-largest drainage basin in the U.S. In Canada, where the Columbia flows for and drains , the river ranks 23rd in length, and its basin ranks 13th in size.

The Columbia shares its name with nearby places, such as British Columbia, as well as with landforms and bodies of water. Columbia Lake, above sea level, and the adjoining Columbia Wetlands form the river's headwaters in the southern Rocky Mountain Trench. The trench is a broad, deep, and long glacial valley between the Canadian Rockies and the Columbia Mountains in British Columbia. For its first , 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 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 centres of the West Kootenay region. The Pend Oreille River joins the Columbia about north of the U.S.–Canada border.