Special Habitats Estuaries Estuaries are bodies of inland freshwater that connect to and mix with saltwater. The unique combination of fresh and saltwater in one place allows estuaries to support an abundance of plant and animal life.
Estuaries can be large, as is the Hudson River.
Or estuaries can be as small as the many tidal creeks emptying marshes on Long Island. They all share the common characteristics that make estuaries ecologically rich, and important to fisheries. Freshwater weighs less than saltwater. Because of this, the freshwater flowing from a river such as the Hudson will float on top of any saltwater entering the river. The saltwater enters the river because the river mouth is below sea level.