The SPARROW Decision Support System (SPARROW DSS) provides access to national, regional, and basin-wide SPARROW models (Spatially Referenced Regressions On Watershed attributes) for water managers, researchers, and the general public. Models are available for a variety of water-quality constituents and time periods. For each model, users can: Map predictions of long-term average water-quality conditions (loads, yields, concentrations) and source contributions by stream reach and catchment Track transport to downstream receiving waters, such as reservoirs and estuaries Evaluate management source-reduction scenarios Overlay land use, shaded relief, street-level data, states, counties, and hydrologic units. Differences among models for the same constituent, time period, and geographical area reflect an evolution of the model applications, technology, and geospatial data as described in supporting documentation.