| Island Park Dam | |
| Dam Crosses: | Henrys Fork |
| Location: | Fremont County, Idaho, near Island Park, Idaho |
| Dam Type: | Zoned earthfill dam |
| Dam Length: | 9500feet |
| Dam Height: | 94feet |
| Spillway Type: | Ungated bathtub |
| Construction Began: | 1937 |
| Opening: | 1939 |
| Operator: | U.S. Bureau of Reclamation |
| Res Name: | Island Park Reservoir |
| Res Capacity Total: | 135205acre.ft |
| Res Catchment: | 482sqmi |
| Location Map: | Idaho |
| Coordinates: | 44.4186°N -111.3965°W |
Island Park Dam is operated by the U.S. Bureau of Reclamation in Fremont County, Idaho, United States. The dam lies in Targhee National Forest near Island Park. The zoned earthfill dam was built between 1937 and 1939 as part of the Minidoka Project, which provides water to irrigate farmland in Idaho's Snake River Plain.[1]
The dam provides only water storage, impounding 135000acre.ft, which is distributed by the Cross Cut Canal to farms in Fremont and Madison counties in Idaho, and Teton County in Wyoming.[1] The Island Park and Grassy Lake reservoirs were built as an alternative to construction of a larger project that would have flooded the Falls River area of Yellowstone National Park.[2] [3]
Island Park Dam has a humid continental climate (Köppen Dfb) bordering upon a subalpine climate (Dfc). Summers feature very warm afternoons and chilly mornings, whilst winters are freezing and very snowy with an annual snowfall averaging 2142NaN2 and reaching 3752NaN2 between July 1974 and June 1975. The dam's weather recording site holds the record for the eighth-lowest temperature recorded in the United States (and lowest temperature recorded in Idaho) at -60F.