The Buffalo Eighteenmile watershed (HUC 04120103) covers approximately 1,076 square miles in southwestern Montana. It is characterized by high-elevation mountains and valleys, with a significant portion of the land area designated as national forest lands. The hydrology of the watershed is dominated by snowmelt and precipitation, with the majority of streamflow occurring in the spring and early summer months. The area experiences a specific snowpack due to its high elevations, with an average snowpack depth ranging from 50-80 inches. Surface water in the watershed is primarily used for agricultural and recreational purposes, with some reservoirs used for hydropower generation. The water quality of the watershed is generally good, with low levels of pollution. In recent years, the area has experienced warming temperatures and decreased snowpack, which has had significant impacts on water resources and ecosystems.