The application of SPARROW for watershed assessment is a new approach that offers three major features when compared to other techniques. First, the statistical basis of SPARROW provides an objective means of identifying relations between stream-water quality and environmental factors such as contaminant sources in the watershed, and land-surface characteristics that affect contaminant delivery to streams. Second, SPARROW's spatially detailed network and traveltime data provide a means of estimating instream-loss rates. These loss rates allow upstream watershed factors to be related to downstream loads in a more integrated way than has been possible previously, and allow the simultaneous evaluation of many factors that affect loads. Third, SPARROW provides a means of retaining detailed spatial information about all environmental factors considered in the regression model. Because the regression models are linked to spatial information, predictions and subsequent analytical results can be illustrated through detailed maps that provide information about nutrient loading at detailed spatial scales.