John Pennekamp Coral Reef State Park is a Florida State Park located on Key Largo in Florida. It includes approximately 70 nautical square miles of adjacent Atlantic Ocean waters. The park is approximately 25 miles in length and extends 3 miles into the Atlantic Ocean along the prominent Hawk Channel passage. It was the first underwater park in the United States. The park was added to the National Register of Historic Places on April 14, 1972.