Fig. 1. Land-cover map of the Potomac River watershed. Classification is based on 2000 Mid-Atlantic Regional Earth Science Applications Center land-cover mapping of the Chesapeake Bay watershed. The percentage of watershed in each cover category is provided in the legend. The triangle indicates the location of the Point of Rocks monitoring station; the circle indicates the approximate location of the Washington, D.C., withdrawal site near Little Falls. PA, Pennsylvania; MD, Maryland; WV, West Virgina; DC, Washington, D.C.; VA, Virgina.