The Eel River is a river in the north part of the U.S. state of California. It flows north about 200 mi (322 km) to the Pacific Ocean, draining 3,684 square miles (9,542 square km). Its largest tributary is the Middle Fork Eel River, followed by the South Fork, Van Duzen River, and North Fork. The river is dammed near its headwaters to divert water into the Russian River valley. The two dams form Van Arsdale Reservoir and the larger Lake Pillsbury. Most of the river is in the humid Coast Ranges of California. Much of the river is isolated, in steep and rugged terrain. 