The North Fork Feather River is a watercourse of the northern Sierra Nevada in the U.S. state of California. It flows generally southwards from its headwaters near Lassen Peak to Lake Oroville, a reservoir formed by Oroville Dam in the foothills of the Sierra, where it runs into the Feather River. The river drains about 2,100 square miles (5,400 km2) of the western slope of the Sierras. By discharge, it is the largest tributary of the Feather. .