Mattawoman Creek is a coastal-plain tributary to the tidal Potomac River with a mouth at Indian Head, Maryland, downstream of Washington, D.C. It comprises a river flowing through Prince George's and Charles counties and a tidal-freshwater estuary in Charles County. About three-fourths of its watershed lies in Charles County, with the remainder in Prince George's County immediately to the north. History Mattawoman appears on Capt. John Smith's circa-1608 map as Mataughquamend, an Algonquian compound translated as “where one goes pleasantly.” Today, Mattawoman Creek is listed by the Environmental Protection Agency (EPA) as impaired under Section 303(d) of the Clean Water Act for excess nutrients, sediment, and loss of living resources. At the same time, because it is the southernmost Potomac River freshwater estuary in Maryland, Mattawoman has escaped much of the degradation associated with urbanization spreading from Washington, D.C. It retains noteworthy biodiversity. Fish Assessments of fish communities throughout the Chesapeake Bay system by the Maryland Department of Natural Resources find the Mattawoman estuary to be the most productive of sampled tributaries for migratory fish. Especially abundant are anadromous alewife, blueback herring and American shad and semi-anadromous white and yellow perch. The largemouth bass, a resident gamefish that supports an active recreational fishery in the tidal freshwater Potomac River and its tributaries, also achieves high concentrations in the estuary. On the basis of fish assessments, Maryland fisheries biologists have concluded that Mattawoman represents as near to ideal conditions as can be found in the northern Chesapeake Bay, perhaps unattainable in other systems, and should be protected from overdevelopment. Marshes The estuary supports extensive freshwater tidal marshes that are partially protected as Maryland Wildlands and as Natural Environment Areas. Palustrine wetlands are concentrated in the broad stream valley of the fluvial reaches, where a site with the greatest species richness of amphibians and reptiles in Maryland has been identified by the Department of Natural Resources. Watershed Mattawoman drains the town of Indian Head, the town of Bryans Road, and most of Waldorf, the largest community in Charles County. Its watershed remains over 50% forested, but it is approaching a 10% impervious cover, often cited as a threshold for significant degradation as measured by water quality and species diversity. Continued loss of forest and increases in impervious cover are anticipated, as most of the watershed in Charles County falls within a designated development district, which at about (214 km2) is larger than