Which is the largest river flowing into the Pacific in North America?

The Columbia River is the largest river flowing into the Pacific Ocean from North America. The Columbia is one of the world’s greatest sources of hydroelectric power and, with its tributaries, represents a third of the potential hydropower of the United States. In addition, its mouth provides the first deepwater harbour north of San Francisco.

The Columbia flows from its source in Columbia Lake, at an elevation of 2,700 feet (820 metres), in British Columbia near the crest of the Rocky Mountains, to the Pacific Ocean at Astoria, Oregon. It drains some 258,000 square miles (668,000 square km), of which about 85 percent is in the northwestern United States. Major tributaries are the Kootenay, Snake, Pend Oreille, Spokane, Okanogan, Yakima, Cowlitz, and Willamette rivers.

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.

Two-fifths of the river’s course, some 500 miles (800 km) of its 1,240-mile (2,000-km) length, lies in Canada, between its headwaters in British Columbia and the U.S. border.