Grassy Lake Dam is a small dam operated by the U.S. Bureau of Reclamation in Teton County, Wyoming, immediately to the south of Yellowstone National Park. The dam lies in a corridor of Bridger-Teton National Forest that runs between Yellowstone and Grand Teton National Parks. The dam structure and outlets are within a few hundred feet of the south boundary of Yellowstone. 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.