Dyke Marsh is a freshwater wetland and wildlife preserve located on the west bank of the Potomac River south of Alexandria, Virginia between Old Town Alexandria and Mount Vernon. Dyke Marsh consists of about of tidal marsh, floodplain, and swamp forest. It formed 5,000 to 7,000 years ago. With a total size of 485 acres, Dyke Marsh is one of the largest remaining pieces of freshwater tidal wetlands left in the Baltimore-Washington Metropolitan Area. The marsh is managed by the National Park Service as part of the George Washington Memorial Parkway. Dyke Marsh contains a wide array of plant and animal life. "Haul Road" is a trail that leads visitors into the marsh. It is frequented by area birdwatchers. Dyke Marsh is located off the George Washington Memorial Parkway at the Belle Haven Marina exit. Here the fresh water of the upper Potomac mixes with the salt water of the lower Potomac. The fresh water tends to float above the tidal salt water producing a tidal freshwater marsh. Name Dyke Marsh got its name because it was within a dike at one point. Earthen walls were built around the perimeter of the marsh in the 19th century to create more "fast land," land not inundated by tides. This land was used for farming purposes, mainly to graze livestock or to grow crops. One of the oldest photographs of Dyke Marsh is a circa 1909 picture postcard created for the Alexandria-Mt. Vernon trolley line (whose light rail tracks were replaced by the George Washington Memorial Parkway in 1932.) The photograph is labelled: The "Dyke," a favorite resort for fishermen and hunters on the line of the Mt. Vernon Railroad, near Alexandria, Va. Wildlife Dyke Marsh has an abundance of wildlife. Evidence of a beaver population is visible along the "Haul Road" and muskrat have been spotted numerous times. Little brown bats and red fox can be seen at night. Cottontail rabbit, gray squirrels, shrews, and field mice (the vole) can also be found in and around the marsh. The most obvious inhabitant of Dyke Marsh is the red-winged blackbird, with its distinct call. The red-winged blackbird nests among the cattails and feeds on insects and seeds. Nearly 300 species of birds have been seen in Dyke Marsh. It is known as one of the best birdwatching sites in the Washington Metropolitan Area. The lower Potomac is a natural migration route, especially