Columbia River Basin (Basin)

Columbia River Basin is an area of about 259,000 square miles that spans seven U.S. states and a portion of southeastern British Columbia. The Columbia River is the main river draining the basin. Major tributaries feeding the Columbia include the Kootenai, Flathead, Clark Fork/Pend Oreille, Kettle, Okanogan, Methow, Spokane, Wenatchee, Yakima, Snake, Clearwater, Salmon, Owyhee, Grande Ronde, Walla Walla, Umatilla, John Day, Deschutes, Hood, Willamette, Klickitat, Lewis, and Cowlitz rivers. The largest tributary, the Snake River, drains an area of nearly 110,000 square miles or almost 50 percent of the U.S. portion of the basin.