AQUATOX is a time-variable ecological risk assessment model that stimulates the fate and effects of various environmental stressors in aquatic ecosystems. It simulates the fate and transfer of pollutants from loads to the water, sediments, and biotic components, and transfer throughout the food web. Simultaneously it predicts the effects of the stressors on the ecosystem, by simulating the chemical, physical and biological processes that bind the ecosystem together. AQUATOX can predict the fate and ecological effects of nutrients, organic toxicants, and bioaccumulative compounds, as well as the expected ecosystem responses to pollution reductions. It considers several trophic levels, including attached and planktonic algae and submerged aquatic vegetation, invertebrates, and forage, bottom-feeding, and game fish; it also represents associated organic toxicants. BASINS (Better Assessment Integrating Point and Nonpoint Sources) is a combined GIS/water quality modeling system that includes numerous national level environmental and cartographic data layers, analytical tools, watershed loading models, and instream water quality models. One of the main advantages of an integrated system such as BASINS is that the time consuming task of developing input data files for the various models is reduced: watershed characteristics necessary for the watershed models can be developed from the landscape data layers, and data can be converted into the proper formats for model input files.