Island Park Reservoir

Overview

Island Park Reservoir which is formed by Island Park Dam is a major feature of the Mindoka Project. Recreation on this 11 square mile (7,000-acre) reservoir with 64 miles of shoreline is administered by the Targhee National Forest. Located in the high country of eastern Idaho, north of Idaho Falls. At Island Park Reservoir, fishing season is year-round for rainbow trout, cutthroat trout, coho salmon, yellow perch, and bluegill. The Island Park area offers excellent trout fishing at Island Park Reservoir and along the Henry's Fork, Buffalo River, Warm River, Fall River and Bitch Creek. Reservoir acre feet and total reservoir capacity and cubic feet/second release rates for rivers below Upper Snake River Basin reservoirs and select river locations are updated daily and graphically provided. Season open year-round.

Island Park Dam is located 38 miles north of Ashton, Idaho, on Henrys Fork. The dam is a zoned earthfill structure 91 feet high. Water stored at Island Park and Grassy Lake Reservoirs is used in Fremont and Madison Counties in northeastern Idaho, and Teton County in Wyoming.

The Upper Snake River Division of the project includes Island Park Dam, Cross Cut Canal and Diversion Dam, and Grassy Lake Dam.

Island Park Reservoir has a total storage capacity of 135,500 acre-feet (active 135,200 acre-feet) which includes 1 foot of surcharge that is filled on a recurring basis and is part of the allocated storage space.

The Safety of Dams modifications were completed at Island Park Dam in the early 1980s. This consisted of replacing the deteriorated concrete in the spillway and excavation and replacement of liquefiable materials in the right abutment.

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