The Big Hole Watershed (HUC 10020004) covers approximately 4,000 square miles in southwestern Montana. The watershed is primarily mountainous, with elevations ranging from 5,000 to over 10,000 feet. The hydrology of the area is heavily influenced by snowpack, as the watershed receives an average snowfall of around 300 inches per year. The snowpack contributes significantly to surface water, including the Big Hole River, which provides important habitat for trout and other aquatic species. The watershed also contains several reservoirs, including Clark Canyon Reservoir, which is used for irrigation and flood control. Interesting climatic facts include the area's reputation for unpredictable weather and frequent snowstorms, as well as a trend of decreasing snowpack in recent years due to climate change. Overall, the Big Hole Watershed is an important ecological and economic resource for the region.