An estuary is formed where fresh water and salt water mix together, creating a dynamic and vital ecosystem. The Albemarle-Pamlico estuary is the second largest estuarine system in the nation. It is composed of seven sounds — Albemarle, Currituck, Croatan, Pamlico, Bogue, Core, and Roanoke sounds. Several river basins drain into the seven sounds, including Chowan, Tar-Pamlico, Neuse, Roanoke, Pasquotank, Perquimans, Little, North, Pungo, Scuppernong and Alligator rivers. The total area drained by the system of rivers and sounds is over 30,000 square miles, including 36 counties in northeastern North Carolina and 16 counties and independent cities in southeastern Virginia.