Watershed management decision support systems are crucial to managing the complexities of locally based planning at the watershed scale including addressing such issues as nonpoint source pollution. CARES at the University of Missouri-Columbia has developed the Watershed Management Decision Support System (WAMADSS), which operates on an IBM RISC/6000 UNIX system. It consists of biophysical simulation models, an enterprise budget generator, and an ARC/INFO geographic information system. Its application has been substantially restricted because users need expensive GIS software and platforms to run WAMADSS. This presentation introduces the current effort at CARES to develop PC-based WAMADSS, which uses ArcView GIS to manipulate social, economic, and geophysical data and integrate it with the Hydrologic Simulation Program-FORTRAN (HSPF) to evaluate environmental impacts of watershed management alternatives. HSPF is developed and maintained by the U.S. Environmental Protection Agency and can be used to simulate the impacts on watershed hydrology, water quality, and stream habitat conditions of both point and nonpoint sources on both urban and nonurban land. ArcView GIS is used to manipulate and process spatial and nonspatial data. Avenue scripting language is used to create a series of graphical user interfaces to streamline the processes and communicate with users. The initial study area is Dardenne Creek watershed in St. Charles and Warren counties, where issues of concern include erosion and sedimentation caused by rapid development, as well as the water quality impacts of agricultural fertilizer and pesticide runoff.