I found some nice information about the area, on their official website :
« Delaware’s Inland Bays, designated an estuary of national significance in 1988, cover 32 square mile and drain a watershed area of about 320 square miles in southeastern Sussex County Delaware. They are separated by a narrow barrier beach from the Atlantic Ocean. Indian River Bay is a shallow drowned river valley system with freshwater inflow and a direct connection to the ocean through the Indian River Inlet. Rehoboth Bay is a shallow coastal lagoon system behind a narrow barrier island. It connects to the ocean by the Lewes and Rehoboth Canal and the Indian River Bay. The smallest and shallowest is Little Assawoman Bay which connects to the ocean via the Ocean City Inlet.
Because they are so shallow, with an average depth ranging from 3 to 8 feet, and because they are poorly flushed by tidal movement, they are especially sensitive to environmental changes. Increases in pollutants, changes in salinity and fluctuations in water temperature, for example, can have dramatic effects on water quality and on the plants, fish, shellfish, and microscopic creatures that live in the bays. »