Dillon Reservoir, Summit co., N central Colo., on Blue R., in Arapaho Natl. Forest, 55 mi/89 km W of Denver; 4 mi/6.4 km long, with 2-mi/3.2-km long SW arm; 39°37'N 106°02'W. Max. capacity of 252,678 acre-ft. Formed by Dillon Dam (240 ft/73 m high), built (1959) by the Denver Water Board for water supply. Harold D. Roberts Tunnel (23 mi/37 km long) delivers water across Continental Divide to North Fork of South Platte R. Resort communities of Dixon and Silverthorne on N shore, near dam, Frisco at SW end.
