Biscayne National Park is a national park of the United States located south of Miami, Florida, in Miami-Dade County. The park preserves Biscayne Bay and its offshore barrier reefs. The shore of the bay is the location of an extensive mangrove forest. The park covers 172,971 acres (69,998.9 ha; 270.3 sq mi; 700.0 km), of which 9,075 acres (3,673 ha) are on land. It includes Elliott Key, the park's largest island and northernmost of the true Florida Keys, formed from fossilized coral reef. The islands farther north in the park are transitional islands of coral and sand. The offshore portion of the park includes the northernmost region of the Florida Reef, one of the largest coral reefs in the world.
Biscayne National Park protects four distinct ecosystems: part of the Florida mangroves along the shoreline, the shallow waters of Biscayne Bay, the coral limestone keys, and the offshore Florida Reef. The shoreline swamps of the mainland and island margins provide a nursery for larval and juvenile fish, molluscs, and crustaceans. The bay waters harbor immature and adult fish, seagrass beds, sponges, soft corals, and manatees. The keys are covered with tropical vegetation including endangered cacti and palms, and their beaches provide nesting grounds for endangered sea turtles. Offshore reefs and waters harbor more than 200 species of fish, pelagic birds, whales, and hard corals. Sixteen endangered species including Schaus' swallowtail butterflies, smalltooth sawfish, manatees, and green and hawksbill sea turtles may be observed in the park. Biscayne also has a small population of threatened American crocodiles and a few American alligators.
