The Estuary System

An estuary is a partially enclosed body of water where fresh water from rivers and streams mixes with salt water from the ocean. Estuaries are among the most productive environments on earth, creating organic matter and providing many different types of habitat that support diverse communities of plants and animals.

The Chesapeake Bay Estuary

Chesapeake Bay is the largest of 130 estuaries in the United States. About half of the Chesapeake's water volume comes from salt water from the Atlantic Ocean. The other half drains into the Bay from its enormous 64,000-square-mile watershed. Because of this mix of fresh and salt water, the Bay's salinity gradually increases as you move from north to south.

Of the 50 major tributaries that flow into the Bay, just three deliver about 80 percent of Bay's fresh water: the Susquehanna River (48 percent), the Potomac River (19 percent) and the James River (14 percent).

Benefits of Estuaries

As a highly productive estuary, the Chesapeake provides an array of critical habitats for thousands of species of fish, birds, mammals and other wildlife.

• Migratory waterfowl stop and feed in wetlands, marshes, open waters and shallow waters during their seasonal flights.
• Anadromous fish like shad and sturgeon spawn in the Bay watershed's freshwater rivers and streams.
• Underwater bay grass beds growing in shallow waters protect juvenile fish and blue crabs, as well as molting blue crabs, from predators.

In addition to serving as wildlife habitat, the wetlands that fringe estuaries also perform valuable functions like filtering polluted runoff, absorbing flood waters and preventing erosion.

Estuaries support educational and family activities like boating, angling, swimming and bird-watching. Estuaries are also commercially important, serving as nursery grounds for commercial fish and shellfish. Chesapeake Bay is home to Baltimore and Hampton Roads, two of the North Atlantic's five major shipping ports.