1 Geology and Geography Geologically speaking, Chesapeake Bay is very young. It was created by the death of the last Ice Age, some 12-18,000 years ago. As the glaciers retreated and the polar ice caps shrank, the huge volume of melting ice caused sea levels to rise. The rising ocean in turn engulfed the coast and flooded the river valley of the ancient Susquehanna river, creating the Chesapeake Bay. The Bay we know today is nearly 200 miles long, fed by 48 major rivers and 100 small tributaries draining a 64,000 square mile basin.
Saltwater mixes into the Bay from the Atlantic Ocean.
Freshwater flows from the Bay's tributary rivers, with about 50 percent coming from the Susquehanna. As a result the Chesapeake ranges from totally freshwater areas in the North and upstream in its rivers, to areas near the Bay's mouth that are about as salty as the ocean. Thus the Bay can support both fresh and marine life forms, plus those that can tolerate fluctuating salinity levels. The variety of conditions supports some 2,700 species. All are linked in a complex, interdependent web of producers and consumers.