This one is called the northern snakehead and the fact that Shank snagged it while fishing at Dam No. 4 south of Downsville was of particular concern to the Maryland Department of Natural Resources. That's because the location is the farthest north on the Potomac River that the snakehead has been found since it was first discovered in the state — in Crofton in Anne Arundel County in 2002 — said Michael T. Kasiwagi, Western II Regional Fisheries Manager for the DNR.