Beginning in British Columbia, the mighty Columbia River flows through Washington state and forms much of the border between Washington and Oregon. The river then flows west and merges with the Willamette River before flowing into the Pacific Ocean. The Columbia River has the largest outflow of any river that empties into the Pacific Ocean. It’s 14 hydroelectric dams make it the nation’s largest hydroelectric producing river.
American explorers Lewis and Clark sailed west on the Columbia River to the Pacific Ocean in 1805. The estuary of the Columbia was so large that they mistook it for the ocean itself.