Because much of the coast and inner estuaries are built by mangroves—and there is no border between the coastal marshes and the bay—the ecosystems in Florida Bay are considered part of the Everglades. More than 800 square miles (2,100 km2) of Florida Bay is protected by Everglades National Park, representing the largest body of water in the park boundaries.[73] There are approximately one hundred keys in Florida Bay, many of which are mangrove forests.[74] Larger islands may be taken over by hardwood hammocks. The outer rims of the Ten Thousand Islands and Cape Sable share characteristics of the intertwining saltwater bays and fresh water marshes.