Brantley Lake is a reservoir on the Pecos River located within Brantley Lake State Park (32.545115°N 104.374403°W / 32.545115; -104.374403) approximately 12 miles (19 km) north of Carlsbad, New Mexico off US 285.It is impounded by Brantley Dam, completed in the 1980s as part of the Brantley Project of the United States Bureau of Reclamation. The project's main purpose was to replace the old McMillan Dam, which had been declared unsafe.