Understanding and predicting fish community interactions and their responses to changes in the environment are critical to the conservation and management of Pennsylvania fish communities and to water resource management. However, quantifying and predicting the effects of environmental stressors on fish communities is made difficult by the complex interactions that exist between species and between species and the environment. As such, accounting for both abiotic drivers and biotic interactions is critical for understanding how changing watershed conditions affect stream communities in Pennsylvania streams. The overall goal of this proposed research is to help inform fisheries and water resource management and conservation by improving our understanding of the relative roles of species interactions, environmental factors, and how species traits influence a species’ response to the abiotic environment in Pennsylvania streams and rivers. To accomplish our goal, we will analyze fish community data from over 2,000 stream and river sites located throughout Pennsylvania. Results from our proposed research will have the capability to address numerous management and conservation questions related to the roles that abiotic stressors and biotic interactions play in structuring Pennsylvania fish communities. An example management outcome is prioritizing stream sites for the reintroduction of native species, based on an understanding of both interacting/competing species and environmental conditions.