Cimarron River, stream that rises near Wheeler Peak in Eagle Nest Lake, Colfax county, northeastern New Mexico, U.S. It flows generally southeastward, joining the Canadian River southeast of Springer after a course of 55 miles (88 km). Eagle Nest Dam (1917), impounding the reservoir at the river’s source, is used for power and irrigation. The river, a popular recreational resource, flows through Cimarron Canyon State Park and the northern portion of Philmont Scout Ranch and is renowned for its trout fishing.