The Guánica Bay/Rio Loco watershed is located in the southwestern corner of Puerto Rico, approximately 20 miles west of the city of Ponce and 100 miles southwest of San Juan. 
Due to human alteration, the watershed is approximately 151 square miles and discharges to Guánica Bay near the town of Guánica. The Guánica Bay/Rio Loco watershed includes the urbanized areas of Yauco and a portion of the Lajas Valley agricultural region. The Guánica Bay/Rio Loco is one of the major riverine discharge points in the southwest coast.
Historically, the area was associated with some of the most pristine reefs on the island.