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Water resources in Puerto Rico are subject to tremendous pressure from urban, industrial, and agricultural activities. As a result, most surface waters exhibit some kind of impact from anthropogenic activities. High P concentrations in surface waters of Puerto Rico suggest this to be the single most important nutrient that must be controlled to reduce the accelerated eutrophication of fresh waters. Although local data is not available, agricultural non-point sources are believed to be the leading cause of nutrient (primarily N and P) and sediment contamination of surface waters. Still, diverse point- and non-point sources such as unsewered communities in urban, suburban, and rural areas, landfills, agricultural activities, and waste-waster treatment facilities have been identified as major contributors of nutrient loads to surface waters in the island. A systematic approach to water quality and watershed restoration must first identify specific contaminant sources as well as characterize their pollution pattern (i.e., relative contribution, seasonal variability, etc). This project reports on an intensive research study to identify and quantify nutrient discharges along the main channel and major tributaries of the Rio Grande de Arecibo Watershed in north central Puerto Rico. It examines seasonal and spatial trends in sediment and nutrient (N and P) concentrations in areas of contrasting land use characteristics. Trends in total P concentrations in water were related to land use, soil test P information, hydrologic discharge, and known point inputs to assess the relative contribution of different sources to the watershed. This information in combination with land use characterization will serve to better delineate the various nutrient contributing sources and establish a targeted nutrient management program for the RGA watershed in the tropical environment of Puerto Rico.