The Florida Keys National Marine Sanctuary is a U.S. National Marine Sanctuary in the Florida Keys. It includes the third-largest coral barrier reef in the world. It also has extensive mangrove forest and seagrass fields. The Marine Sanctuary includes a 2,800 square nautical mile (9,604 km²) area surrounding the Keys and reaching into the Atlantic Ocean, Florida Bay and the Gulf of Mexico. The Sanctuary was established in 1989.