The report characterizes a 0.43-square-mile agricultural watershed in York County, underlain by albite-chlorite and oligoclase-mica schist in the Lower Susquehanna River basin, that is being studied as part of the U.S. Environmental Protection Agency's Chesapeake Bay Program. The water quality of Bald Eagle Creek was studied from October 1985 through September 1987 prior to the implementation of Best-Management Practices to reduce nutrient and sediment discharge into Muddy Creek, a tributary to the Chesapeake Bay. About 88 percent of the watershed is cropland and pasture, and nearly 33 percent of the cropland is used for corn. The animal population is entirely dairy cattle. About 85,640 pounds of nitrogen (460 pounds per acre) and 21,800 pounds of phosphorus (117 pounds per acre) were applied to fields; 52 percent of the nitrogen and 69 percent of the phosphorus was from commercial fertilizer. Prior to fertilization, nitrate nitrogen in the soil ranged from 36 to 136 pounds per acre and phosphorus ranged from 0.89 to 5.7 pounds per acre in the top 4 feet of soil. Precipitation was about 18 percent below normal and streamflow about 35 percent below normal during the 2-year study. Eighty-four percent of the 20.44 inches of runoff was base flow. Median concentrations of total nitrogen and dissolved phosphorous in base flow were 0.05 and 0.04 milligrams per liter as phosphorus, respectively. Concentrations of dissolved nitrate in base flow increased following wet periods after crops were harvested and manure was applied. During the growing season, concentrations decreased similarly to those observed in carbonate-rock areas as nutrient uptake and evapotranspiration by corn increased. About 4,550 pounds of suspended sediment, 5,250 pounds of nitrogen, and 66.6 pounds of phosphorus discharged in base flow during the 2-year period. The suspended sediment load was about 232,000 pounds in stormflow from 26 storms that contributed 51 percent of the total stormflow. The nitrogen load was about 651 pounds and the phosphorus load was about 74 pounds in stormflow from 16 storms that contributed 28 percent of the total stormflow. It is estimated that concentrations of total nitrogen and phosphorus in base flow need to be reduced by 12 and 48 percent, respectively, to detect changes during the nutrient-management phase. Likewise, loads to total nitrogen and phosphorus in base flow need to be reduced by 62 and 57 percent.