Derby Dam is a diversion dam on the Truckee River, located between Reno and Fernley in Storey and Washoe counties in the U.S. state of Nevada. It diverts water that would otherwise feed Pyramid Lake into the Carson River watershed for irrigation use. It is operated by the Truckee-Carson Irrigation District. The dam was named after the Derby Southern Pacific Railroad station.The project was authorized by Ethan A.