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.
Towns along the Eel include Ferndale, Rio Dell, and Dos Rios (at the confluence with the Middle Fork). Weott is near the South Fork confluence.
U.S. Highway 101 follows the river until the South Fork confluence, and the Great Northern Railway also follows a portion of the river. 37 bridges cross the Eel and 24 cross the South Fork. The South Fork is the longest tributary. The Middle Fork has the largest watershed.