Beaver Creek is a tributary of the Des Moines River that rises at the northern border of Boone County in the U.S. state of Iowa, and then flows generally south and southeast through western Boone County, northeastern Dallas County, and finally northwestern Polk County before flowing into the Des Moines River approximately a mile south of the Saylorville Reservoir in Polk County. In total, the main channel is approximately 77 miles (124 km) in length, and the watershed drains approximately 380 square miles (980 km2).