Fremont River (Sevier/Wayne) originates at the Johnson Valley Reservoir north of Fishlake and drains southeast to combine with the Muddy River at Hanksville. It then forms the Dirty Devil River. On July 27, 1869, the Powell expedition discovered an unknown river at the mouth of Narrow Canyon on the Colorado River. They named the river the Dirty Devil, but did not indicate how far up the river the name would apply, nor did they know that the river branched out. Subsequent conflicting claims forced the renaming of the upper portions of the Dirty Devil. Today the two main branches of the Dirty Devil are the Muddy and the Fremont rivers.