Flathead Catfish records in the Atlantic Slope drainage of Pennsylvania date back to the early 1990s; however, large-scale range expansion and population increases were not realized until the late 1990s in the Delaware River drainage and the early 2000s in the Susquehanna River drainage. The impacts of introduced Flathead Catfish on migratory and resident fishes are well documented. Models suggest that Flathead Catfish suppress native fish biomass 5 – 50% through predation and competitive interactions. The purpose of this project is to estimate the density and distribution of invasive Flathead Catfish in the mainstem Susquehanna River and select tributaries. Resultant data will serve to develop current distribution, understand population characteristics, and to populate models currently being developed and implemented in the Chesapeake Bay as part of the NOAA Sustainable Fisheries Goal Implementation Team (GIT), Invasive Catfish Taskforce and Pennsylvania Fish and Boat Commission (PFBC) Catfish Management Plan.