Foster Creek, a freshwater tidal creek in Berkeley County, South Carolina, is located in an area of potential contaminant sources from residential, commercial, light industrial, and military activities. The creek is used as a secondary source of drinking water for the surrounding Charleston area. Foster Creek meets most of the freshwater- quality requirements of State and Federal regulatory agencies, but often contains low concentrations of dissolved oxygen and has been characterized as eutrophic. Investigations of water- and bed-sediment quality were made between 1991 and 1993 to assess the effects of anthropogenic sources of contamination on Foster Creek. Low-flow surface-water samples were generally free of toxic compounds with the exception of laboratory artifacts and naturally occurring trace metals. Storm-runoff samples generally contained very low concentrations (near detection limits) of a small number of volatile and semivolatile organics and naturally occurring trace metals. Concentrations of toxic compounds in excess of current (1995) South Carolina Department of Health and Environmental Control and U.S. Environmental Protection Agency regulations were not detected in surface-water samples collected from Foster Creek. Chemical analyses of streambed sediments indicated minimal anthropogenic effects on sediment quality. The particle-tracking option of the U.S. Geological Survey one-dimensional unsteady-flow model (BRANCH) indicated that as the simulated volume of rainfall runoff increased in the Foster Creek Basin, simulated particles in Foster Creek were transported greater distances. Simulating flow through the Bushy Park Dam (also known as Back River Dam) had little effect on particle movement in Foster Creek. Simulating typical withdrawal rates at a water-supply intake resulted in a slight attraction of particles toward the intake during conditions of relatively low runoff. These withdrawals had a greater influence on particles downstream of the intake than on those upstream of the intake. Simulations confirmed earlier findings which suggested that the creek would not flush during baseflow conditions, with the exception of the lower 1-mile reach, where flushing results from tidal movements. According to the simulations, Foster Creek will fully flush if a 2-year, 7-day storm occurs. Flushing appears to be affected more by the total volume of storm runoff than by typical municipal withdrawals or tidal effects.