The Casselman River is a 56-mile-long river that flows through Maryland and Pennsylvania, serving as a tributary to the Youghiogheny River. Beginning in Garrett County, Maryland with two forks that meet at Grantsville, the river flows northward into Pennsylvania before joining the Youghiogheny near Confluence, PA. The river features a relatively slow and steady flow with a low gradient as a freestone waterway. The Maryland section of the Casselman has better water quality than the Pennsylvania section, as significant efforts have been made to mitigate acid mine drainage impacts in Maryland. Despite water quality challenges in Pennsylvania from coal mine drainage and other pollution sources, the river supports diverse fish populations and offers excellent fishing opportunities throughout its course.