Observations of the physical, chemical, and biological water quality of five streams draining to the tidal Potomac River and Estuary during the 1979-81 water years are tabulated. The streams sampled are Rock Creek, the Northwest and Northeast Branches of the Anacostia River, the Occoquan River, and St. Clements Creek. Samples, usually collected during storms, were routinely analyzed for sediment, biochemical oxygen demand, dissolved silica, and the total and dissolved forms of phosphorus and of nitrogen species. Additional analyses for specific conductance, chlorophyll-a, and phytoplankton abundance and generic composition were done on a few samples taken during the 1980 water year. Observations of water temperature were made during the same period. Selected measurements of the turbidity of the raw water intake for the Occoquan Water Treatment Plant also are included. (Author 's abstract)