The Antelope Fremont Valleys watershed (HUC 18090206) covers approximately 1,313 square miles in south-central Idaho. The region is primarily dominated by high desert landscapes, with the mountains to the north receiving the majority of the annual precipitation. The hydrology of the watershed is characterized by the Snake River Plain aquifer system, which supplies much of the water for irrigation and municipal use. The region experiences a continental climate, with hot summers and cold winters. Snowpack is important for water supply in the region, with the Upper Snake River Basin snowpack reaching its maximum typically in April. Surface water in the watershed includes the Snake River, streams, and numerous reservoirs, including American Falls Reservoir and Palisades Reservoir. Interesting climatic trends include increasing temperatures and decreasing snowpack, both of which could have significant impacts on water supply in the region.