We surveyed freshwater and oligohaline portions of tidal river systems in Delaware, the eastern shore of Maryland, and southern New Jersey for native and introduced Phragmites australis populations. Populations of native P. australis occur along the major rivers of the eastern shore of Maryland, particularly the Choptank and Nanticoke Rivers, and were common along river and creek edges and typically less dense than introduced P. australis. In contrast, few native populations occur along rivers in Delaware and southern New Jersey where introduced P. australis dominates. These differences in distribution of native P. australis could be due to the magnitude of human impacts and the timing of invasion of introduced P. australis into these systems. The presence of so many populations of native P. australis on the eastern shore of Maryland is unique today as the subspecies has all but disappeared from much of its historical range along the Atlantic Coast.