At the global scale, the population density of coastal areas is nearly three times that of inland areas, and consequently, land development represents a threat to coastal ecosystems. It is critical to understand how increasing urbanization affects coastal watersheds. To that end, the objective of this study was to examine the influence of urban development on stream water quality and hydrology in a coastal setting, a scenario that has received less attention than other physiographic regions. Stream hydrologic, physicochemical, and microbial data were collected in watersheds near Apalachicola, Florida with a range of impervious surfaces from 0 to 15%. Watersheds with greater impervious cover exhibited higher pH, specific conductance, and temperature, elevated nutrient concentrations and loads (Cl À , NO 3 À , SO 4 2À , Na + , K + , Mg 2+ , Ca 2+ , and total phosphorus), higher bacterial concentrations (fecal coliform and Escherichia coli), and increased maximum flow and hydrograph flashiness. Different responses to development here compared to other physiographic regions included lower total suspended solid concentrations, higher total dissolved solid concentrations, and a lack of response of base flow to increased urbanization. Additionally, Na + and Cl À concentrations were elevated to a greater extent than is often the case in non-coastal areas. In the coming years, urban development is projected to increase substantially in coastal zones and thus there is risk of further stream degradation in coastal watersheds.Significant difference among IS classes indicated by different letters. † p = 0.07 TP = total phosphorus, DOC = dissolved organic carbon, TDN = total dissolved nitrogen, TSS = total suspended solids, and TDS = total dissolved solids.URBANIZATION EFFECTS ON WATER RESOURCES † Total forest includes evergreen, mixed, and forested wetlands. NS indicates the relationship was not significant at the 0.05 probability level. TP = total phosphorus, DOC = dissolved organic carbon, TDN = total dissolved nitrogen, TSS = total suspended solids, and TDS = total dissolved solids. R. C. NAGY ET AL Q avg = average flow, Q min = minimum flow, Q 0.1% = flow exceeded 99.9% of the time, Q 1% = flow exceeded 99% of the time, Q 50% = median flow, Q max = maximum flow, RB = flashiness index, and BF = base flow. R. C. NAGY ET AL