A vital waterway of the Pacific Northwest. Rising in the Rockies of British Columbia, the Columbia flows through Lake Revelstoke before entering Washington state. Grand Coulee Dam along the Columbia in Washington forms Lake Roosevelt. When it was completed in 1943, Grand Coulee was the largest hydroelectric plant in the world; it is still America's largest electric power plant. The Columbia receives the Yakima and Snake Rivers before forming much of the Washington-Oregon border, receiving the Willamette River in Portland before emptying into the Pacific where Lewis and Clark sighted the ocean.