Biscayne National Park is an American national park located south of Miami, Florida in Miami-Dade County. 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 and includes Elliott Key, the park's largest island and northernmost of the true Florida Keys, formed from fossilized coral reef.