The Sun Watershed (HUC 10030104) covers an area of approximately 1,900 square miles in eastern Idaho. The watershed is predominantly mountainous and includes the Big Hole Range and the southern portion of the Lemhi Range. The hydrology of the watershed is heavily influenced by snowpack, with up to 80% of annual streamflow derived from snowmelt. Average annual precipitation ranges from 12-18 inches, with the majority falling as snow in the winter months. The watershed contains several surface water bodies, including Sun Valley Lake and Warm Springs Creek. These water bodies are used for recreational purposes and also provide irrigation water for local agriculture. Reservoir constituents include trout and other fish species. Interesting climatic facts include the area's high elevation and the influence of the Pacific Ocean on weather patterns. Recent trends indicate a decrease in snowpack and earlier snowmelt due to climate change.