Mortalities of young-of-the-year (YOY) smallmouth bass (Micropterus dolomieu) recently have occurred in the Susque-hanna River due to Flavobacterium columnare, a bacterium that typically infects stressed fish. Stress factors include but are not limited to elevated water temperature and low dis-solved oxygen during times critical for survival and devel-opment of smallmouth bass (May 1 through July 31). The infections were first discovered in the Susquehanna River and major tributaries in the summer months of 2005 but also were prevalent in 2007.