The Estuary System

An estuary is a partially enclosed body of water where fresh water from streams and rivers mixes with salt water from the ocean. Estuaries are among the most productive environments on earth, creating organic matter and providing a variety of habitats that support diverse animal and plant communities.

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 Chesapeake Bay, just three deliver about 80 percent of the Bay's fresh water:

• The Susquehanna River (48 percent)
• The Potomac River (19 percent)
• The James River (14 percent)

Benefits of Estuaries

As a highly productive estuary, the Chesapeake Bay has an array of critical habitats that thousands of species of fish, birds, mammals and other wildlife depend on for their survival.

• Migratory waterfowl stop and feed in the Bay's wetlands, marshes, open waters and shallow waters during their seasonal flights.
• Anadromous fish such as shad and sturgeon spawn in the Bay's freshwater rivers and streams.
• Underwater bay grass beds growing in the Bay's 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 perform valuable functions such as filtering polluted stormwater runoff, absorbing flood waters and preventing erosion.

Estuaries are important to people, too.

• Estuaries support educational and family activities such as boating, angling, swimming and bird-watching.
• Enjoy catching (and eating) striped bass, perch, flounder or croaker? These fish all depend on estuaries for part or all of their lives. Estuaries provide habitat, including spawning and nursery grounds, for 80 to 90 percent of America's recreational fish catch and more than 75 percent of the commercial fish catch.
• The Chesapeake Bay estuary is home to Baltimore and Hampton Roads, two of the North Atlantic's five major shipping ports.