Biscayne Bay (bĬskān´), shallow, narrow inlet of the Atlantic Ocean, c.40 mi (60 km) long, SE Fla. Famous resort areas, including Miami and Miami Beach, are on the NW and NE respectively. Tourism is the economic mainstay. Many varieties of tropical fish as well as sponges, sea turtles, and the endangered manatee inhabit the waters of the bay. Biscayne National Park, originally Biscayne National Monument (est. 1968), is at its southern end (see National Parks and Monuments, table).