The Beaver River is the historic name for an intermittent river in Oklahoma that drains most of the Oklahoma Panhandle. It is also known as the North Canadian River; both names are in common use. The Beaver River flows from Union County, New Mexico, entering the Oklahoma Panhandle in Cimarron County, then flowing out of state through Sherman County in the Texas Panhandle for about 15 miles (24 km), then back to the Oklahoma panhandle in Texas County, where it is impounded in Optima Lake.