BASINS is a multipurpose environmental analysis system for use by regional, state, and local agencies in performing watershed- and water-quality-based studies. BASINS comprises a suite of interrelated components for performing the various aspects of environmental analysis. The six components include (1) nationally derived databases with Data Extraction tools and Project Builders; (2) assessment tools (TARGET, ASSESS, and Data Mining) that address large- and small-scale characterization needs; (3) utilites to facilitate organizing and evaluating data, including Watershed Delineation, Import, Land Use Reclassfication, and DEM Reclassification; (4) Watershed Characterization Reports that facilitate compilation and output of information on selected watersheds; (5) water quality models including TOXIROUTE and QUAL2E; and (6) the Nonpoint Source Model (NPSM) and postprocessor, which provide integrated assessment of watershed loading and transport, The assessment component, working under the GIS umbrella, allows users to quickly evaluate selected areas, organize information, and display results. The modeling component module allows users to examine the impacts of pollutant loadings from point and nonpoint sources.