Fish communities in river networks provide significant ecosystem services that will likely decline under future land use and climate change. We eveloped a model that simulates the consequences to multiple populations of one or more fish species-a metacommunity-from multiple stressors across a river network. The model is spatiallyexplicit and age-structured, with three components: habitat suitability; population dynamics, including species interactions; and movement across a spatial network. Although this model is simple, it can form the basis of fisheries assessments and may be incorporated into an integrated modeling system for watershed management and prediction.