Excess phosphorus in surface water can cause eutrophication and degrade water quality. Little is know about the impact of suburban landscapes on water quality. Suburban areas continue to grow in the Northeast United States, making their role in water quality protection of paramount importance. Runoff collected from 98 precipitation events and three landscapes in a developed watershed in Ithaca, NY was analyzed for dissolved P (DP), particulate P (PP) and total P (TP) and mass losses calculated. Monitored landscapes, arranged in a randomized complete block design, included low and high maintenance lawns, and wooded areas. Stream gauges were installed at the stream entrance to the developed area and the watershed outlet to monitor the impact of the landscapes on stream water quality. The most important factor to consider when assessing landscape impact on water quality is location. Areas closer to the watershed outlet had an order of magnitude more runoff, and higher P losses than areas higher in the watershed. Controlling for location, unfertilized lawns had the highest runoff losses, followed by wooded areas, and fertilized lawns. Dissolved P, PP, and TP losses were not significantly different between landscapes over the study period. However, covariance modeling indicates that individual landscapes, or groups of landscapes show strong covariation with the P status in the stream. Phosphorus mass losses in the stream are highly covariate with P mass losses from the lower watershed landscapes, while P concentrations (particularly PP and TP) are covariate with P concentrations from the wooded areas. Analysis of stream flow data further indicates that the developed area increases DP, PP, and TP concentrations and mass losses in the stream. These results indicate that it is imperative to assess landscape performance and suitability to reduce contamination of surface water.