The Chesapeake Bay is the largest body of water in Maryland. Maryland also has nearly 50 rivers and creeks, plus streams, ponds, man-made lakes and the Atlantic Ocean. These waterways have been sources of food, employment, transportation and recreation for many centuries.

The major source of the Chesapeake Bay is the Susquehanna River. It is now the largest non-navigable river in North America, but 20,000 years ago, the Susquehanna flowed all the way from upstate New York to the Atlantic Ocean. Ten thousand years ago, melting glacier ice caused the Atlantic to rise and push up into the Susquehanna; overflowing its banks and creating the Chesapeake Bay.

The Bay is a drowned river bed of the Susquehanna River and also an estuary, where fresh and salt water mingle. The "watershed: or "drainage area" of the Bay T-includes the area of land and rivers from Cooperstown, New York to Virginia.