The Elm Fork of the Trinity River runs through Denton County

The Elm Fork is one of the main branches of the Trinity River. It flows south through Denton County. Two major reservoirs sit on this river: Ray Roberts Lake, formed by a dam completed in 1987, and Lake Lewisville downstream, which traces back to a dam built in the 1920s that originally formed Lake Dallas. Both reservoirs serve as drinking water supplies for millions of DFW residents.

The Elm Fork bottomlands are prone to flooding after heavy rains. FEMA maps along its banks show Special Flood Hazard Areas in multiple communities. The Greenbelt Corridor connecting Ray Roberts Lake to Lake Lewisville follows the river and is part of Ray Roberts Lake State Park.