George Boxall is currently working with the Environmental Protection Agency to develop a spatially explicit, multi species fish population model. The model allows users to determine the grain and extent of river networks within which fish populations reproduce, move, and survive. Movement, fecundity and survival are affected by both environmental drivers and assemblage interactions. Users can define fish population responses to environmental factors such as streamflow, temperature and gradient as well as the effect of predation and competition. Each life stage of a species can be parameterized and tracked uniquely. The model can be used to predict the response of fish assemblages under a range of future and present land use scenarios or as a decision support tool for stakeholders. Currently the model is being applied to the Willamette River basin of Oregon but can easily be adapted to other systems.