The South Fork Republican River is a river that arises in Lincoln County, Colorado, United States, and flows east-northeastward for about 171 mi through Kit Carson and Yuma Counties, Colorado, and Cheyenne County, Kansas, to a confluence with the Republican River in Dundy County, Nebraska. Bonny Reservoir is located on the South Fork Republican River in Yuma County, Colorado. The South Fork Republican River drains an area of 2778 sqmi, including 2106 sqmi, or 75.8%, in eastern Colorado, 667 sqmi, or 24.0%, in northwestern Kansas, and 6 sqmi, or 0.2%, in southwestern Nebraska. Use of water from the South Fork Republican River is governed by the Republican River Compact, a water agreement among the U.S. states of Colorado, Kansas Nebraska signed on 12-31-1942