Urbanization poses a particular threat to the coastal areas of the southeastern United States where uplands surrounding wetlands are still relatively undeveloped compared with other regions. Predictive models, which would correlate information on land use change and development, would be useful so that downgrades in water quality can be predicted before they occur to allow effective land management decisions to be made. The approach used for this study involved a historical comparison of land use change and fecal coliform bacterial densities on Murrells Inlet (MI) (urbanized site) (n = 2026 samples) and North Inlet (NI) (pristine site) (n =1656 samples), both bar-built estuaries located on the northern coast of South Carolina south of Myrtle Beach. The microbiological and water quality data used in this research covered the period of 1967–1995 and the following parameters were used: date of sampling, most probable number (MPN) of fecal coliform bacteria, salinity, rainfall and water temperature. The regression models used the above parameters and a change in trend term that accounted for both instantaneous and gradual changes in water quality that may arise from a particular environmental intervention. For MI, the 1980 environmental intervention consisted of the construction of a jetty and the conversion from septic tanks to a main sewer line of approximately 92% of all residences. For NI, the 1973 and 1977 interventions were the construction of Baruch Laboratory and urban development of Debidue Island, respectively. For MI, the intervention, controlling for other environmental parameters, was found to be significant at the alpha = 0.05 level. There was a significant decrease in the increasing trend of fecal coliform bacteria for MI and the conversion to the sewage collection system had a beneficial effect on water quality and probably dominated the jetty effect. For NI, the laboratory construction had no overall impact on water quality so background natural sources of bacteria probably masked any small increases from human sources.