In western Pennsylvania, flathead catfish are native to the Ohio, Allegheny and Monongahela river watersheds. Flathead
catfish populations have since been introduced to eastern PA waters where they are not native. They were first confirmed at Blue Marsh Reservoir in 1997, based on the age and
size of the fish taken, it's likely flatheads had been in the reservoir for some time. Since then flatheads have spread to other non-native waters, including the Schuylkill, Delaware and Susquehanna rivers.....more.