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.