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 dam provides only water storage, impounding 15,200 acre feet (0.0187 km3). Given the small catchment area of Grassy Creek, inflow is augmented by a 0.7-mile (1.1 km) ditch that moves water from Cascade Creek into the reservoir.