Mattawoman Creek
 Mattawoman Creek is a 30.0-mile-long (48.3 km) coastal-plain tributary to the tidal Potomac River with a mouth at Indian Head Maryland 20 miles (32 km) downstream of Washington D.C. It comprises a 23-mile (37 km) river flowing through Prince George's and Charles counties and a 7-mile (11 km) tidal-freshwater estuary in Charles County. About three-fourths of its 94-square-mile (240 km2) watershed lies in Charles County with the remainder in Prince Georges County immediately to the north.