The Prairie Willow watershed spans over 1,500 square miles in southwestern Montana and northern Wyoming. It is part of the Yellowstone River Basin and is fed by snowpack and precipitation. The watershed is home to several small streams and rivers that flow into the Yellowstone River, including the Clarks Fork River and Rock Creek. The snowpack in the watershed varies from year to year, with some years experiencing high snowpack levels that contribute to spring flooding. The surface water in the watershed is used for irrigation and supports agricultural activities in the area. The reservoirs in the watershed include the Buffalo Bill Reservoir, which is used for flood control and irrigation. The area experiences a semi-arid climate, with average annual precipitation ranging from 9-14 inches. In recent years, the area has experienced a trend of decreasing snowpack and earlier snowmelt, which impacts water availability in the watershed.