Lake Oroville is a reservoir formed by the Oroville Dam impounding the Feather River, located in Butte County, northern California. The lake is situated 5 miles northeast of the city of Oroville, within the Lake Oroville State Recreation Area, in the western foothills of the Sierra Nevada. Known as the second-largest reservoir in California, Lake Oroville is t…Lake Oroville is a reservoir formed by the Oroville Dam impounding the Feather River, located in Butte County, northern California. The lake is situated 5 miles northeast of the city of Oroville, within the Lake Oroville State Recreation Area, in the western foothills of the Sierra Nevada. Known as the second-largest reservoir in California, Lake Oroville is treated as a keystone facility within the California State Water Project by storing water, providing flood control, recreation, freshwater releases to assist in controlling the salinity intrusion into the Sacramento-San Joaquin Delta and protecting fish and wildlife.