Vicinity watercourses include the Stanislaus River, the Tuolumne River and Dry Creek empties into the Tuolumne River. Area groundwater, which is the principal source of water supply in the city, has been historically impaired in a fashion that is spatially variable. Water from the nearby Modesto Reservoir is now used to augment city water. In various parts of the city and its perimeter the following water pollutants have occurred from time to time: nitrates, dibromochloromethane, volatile organics, salinity, total dissolved solids and other pesticides. Each of these contaminants is not present citywide.