SPARROW (SPAtially Referenced Regressions On Watershed attributes) mappers are interactive tools that allow the user to explore river streamflow, nutrient contents, sediment loads throughout the riverbed, river yields, and the importance of different sources of contaminants and pollutants in a particular river basin. Data can be visualized using maps, interactive graphs, tables, rankings, and reports that can be shown by state, major watershed, hydrologic unit (HUC), and catchment. These mappers simulate streamflow and constituent loads that would occur under long-term average hydrologic conditions, for the time period 1999 through 2014, and source inputs that occurred during or near the 2012 year.