Precipitation data were collected at 46 precipitation sites and 3 atmospheric deposition sites, and hydrologic data were collected at 6 stream sites in the vicinity of Charlotte and Mecklenburg County, North Carolina, from July 1997 through September 1998. Data were collected to identify the type, concentration, and amount of nonpoint-source stormwater runoff in the study area. The data collected include measurements of precipitation; streamflow; physical characteristics, such as water temperature, pH, specific conductance, biochemical oxygen demand, oil and grease, and suspended-sediment concentrations; and concentrations of nutrients, metals and minor constituents, and organic compounds. These data will provide information needed for (1) planned watershed simulation models, (2) estimates of nonpoint-source constituent loadings to the Catawba River, and (3) characterization of water quality in relation to basin conditions. Streamflow and rainfall data have been used to provide early warnings of possible flooding.