The Eel River (Cahto: Taanchow) is a major river, about long, of northwestern California in the United States. The river and its tributaries form the third largest watershed entirely in California, draining a rugged area of in five counties. The river flows generally northward through the Coast Ranges west of the Sacramento Valley, emptying into the Pacific Ocean about downstream from Fortuna and just south of Humboldt Bay. The river provides groundwater recharge, recreation, and industrial, agricultural and municipal water supply.