<Tr> <Td_colspan="2"> Columbia River drainage basin </Td> </Tr> <Tr> <Td_colspan="2"> Wikimedia Commons: Columbia River </Td> </Tr> <P> The Columbia River is the largest river in the Pacific Northwest region of North America . The river rises in the Rocky Mountains of British Columbia, Canada . It flows northwest and then south into the US state of Washington, then turns west to form most of the border between Washington and the state of Oregon before emptying into the Pacific Ocean . The river is 1,243 miles (2,000 km) long, and its largest tributary is the Snake River . Its drainage basin is roughly the size of France and extends into seven US states and a Canadian province . The fourth - largest river in the United States by volume, the Columbia has the greatest flow of any North American river entering the Pacific . </P> <P> The Columbia and its tributaries have been central to the region's culture and economy for thousands of years . They have been used for transportation since ancient times, linking the region's many cultural groups . The river system hosts many species of anadromous fish, which migrate between freshwater habitats and the saline waters of the Pacific Ocean . These fish--especially the salmon species--provided the core subsistence for native peoples . </P>

What river forms part of the border between two northwestern states and flows into pacific ocean