Built between 1935 and 1939, Grassy Lake Dam is 118 feet (36 m) high with a capacity of 15,200 acre feet (0.0187 km3) on Grassy Creek. Grassy Creek's flow was not sufficient to supply the reservoir reliably, so water from Cascade Creek was diverted by a 14 feet (4.3 m) dam and diversion canal 0.7 miles (1.1 km) long.[2] The lands around Grassy Lake and Island Park Reservoirs are administered by the U.S. Forest Service.[1] Island Park Dam on the Henrys Fork of the Snake River, 38 miles (61 km) north of Ashton, Idaho.