The Susquehanna River Twenty thousand years ago, during the last Ice Age, sea level was about 330 ft. lower than it is today. At that time, the Susquehanna flowed from the edge of the polar ice cap (in what is now north central Pennsylvania) down to the Atlantic. All of the rivers in what is now the Chesapeake drainage basin flowed into it. As the earth warmed up and sea level rose, the Atlantic backed up into the Susquehanna's valley floor, forming the Chesapeake Bay and the tidal portions of rivers like the Potomac and the Nanticoke. The Chesapeake Bay is essentially the tidal portion of the Susquehanna. The River and the Bay are two integral parts of one ecosystem.
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