Biscayne National Park is an American national park in southern Florida, south of Miami. The park preserves Biscayne Bay and its offshore barrier reefs. Ninety-five percent of the park is water, and the shore of the bay is the location of an extensive mangrove forest. The park covers 172,971 acres (270.3 sq mi; 700.0 km2) and includes Elliott Key, the park’s largest island and first 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: the shoreline mangrove swamp, 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.