Earth and water continue to compete for this territory, redrawing the shoreline as land is built up in some areas and lost beneath waves in other places. People have also redrawn shorelines, often on a much faster scale than nature. Excessive clearing and poor land management have increased upland erosion, sending tons of sediment downstream. As a result, communities that were once important ports are now landlocked. On the other side, the construction of seawalls and breakwaters has interfered with the natural flow of sand, causing beaches to rapidly erode.
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.