The
Florida Reef (also known as the
Great Florida Reef,
Florida reefs,
Florida Reef Tract and
Florida Keys Reef Tract) is the only living
coral barrier reef in the continental United States. It is the third largest coral barrier reef system in the world (after the
Great Barrier Reef and
Belize Barrier Reef). It lies a few miles seaward of the
Florida Keys, is about 4 miles (6 to 7 km) wide and extends (along the 20 meter depth contour) from
Fowey Rocks just east of
Soldier Key to just south of the
Marquesas Keys. The barrier reef tract forms a great arc, concentric with the Florida Keys, with the northern end, in
Biscayne National Park, oriented north-south and the western end, south of the Marquesas Keys, oriented east-west. The rest of the reef outside Biscayne National Park lies within
John Pennekamp Coral Reef State Park and the
Florida Keys National Marine Sanctuary. Isolated coral patch reefs occur northward from Biscayne National Park as far as
Stuart, in
Martin County. Coral reefs are also found in
Dry Tortugas National Park west of the Marquesas Keys. There are more than 6,000 individual reefs in the system. The reefs are 5,000 to 7,000 years old, having developed since sea levels rose following the
Wisconsinan glaciation.