area of coral reefs and other marine features in the Atlantic Ocean off the southeastern coast of Florida, U.S., about 20 miles (32 km) south of Miami. Authorized as Biscayne National Monument in 1968 (with a boundary change in 1974), it became a national park in 1980. The park protects the northernmost group of living coral reefs in the United States and their ecosystem. Its surface area is 270 square miles (699 square km), 95 percent of which is water.

The park lies at the northern end of the Florida Keys, between Key Biscayne to the north and Key Largo to the south. It consists of (from west to east) a mangrove-covered shoreline, the shallow Biscayne Bay, about 33 keys (or islands) that form a north-south chain separating the bay from the Atlantic Ocean, and the underwater coral reefs in the Atlantic. A relatively narrow strip of mainland shoreline (0.5 to 1 mile 【1 to 1.5 km】 wide), interrupted by a nuclear power plant at Turkey Point in the southwest, forms most of the western boundary of the park and is the location of park headquarters. This shoreline is covered by an almost unbroken, nearly impenetrable mangrove swamp, which provides shelter for birds, mammals, and marine life. Biscayne Bay, with a maximum depth of about 12 feet (4 metres), supports underwater sea grass beds inhabited by shrimps, lobsters, fishes, sea turtles, and manatees. The chain of keys along the eastern edge of the bay are fringed by mangroves; the interiors of these islands are covered by tropical hardwood forests, with a variety of trees and shrubs common to the West Indies. In the Atlantic Ocean to the east of these keys lie the shallow-water reefs noted for both their variety of corals—elkhorn, brain, and staghorn—and their brilliantly coloured tropical fishes—wrasse, angelfish, and goby. These reefs support more than 200 types of fishes.

Access to the park is by boat (private or commercial), with glass-bottomed boat rides available for viewing the coral reefs. Camping is permitted on some of the keys, and some have overnight anchorage sites located offshore.