Lake Gregory is a reservoir in the San Bernardino National Forest of the San Bernardino Mountains in San Bernardino County, California. The lake and the surrounding area make up the Lake Gregory Regional Park adjacent to Crestline, California. A road built over the dam (present-day Lake Drive) completed the project in January 1939. Private vessels and power boats are not allowed on Lake Gregory, although rowboats, paddle boards, pedal-powered "water trikes" and paddle boats are available for rental. The rowboats may be affixed with the renter's own electric trolling motor.