While wade fishing below the Livingston dam many years ago ( the cable used to be about 45 yards from the riprap) a friend of mine and myself heard a bunch of folks shouting from the boats anchored at the cable who were pointing behind us. We turned to see a FIN about 50 yards downstream from us, it appeared to be a dorsal fin from about a 5'+ shark. It hovered a bit then submerged, we keep fishing(big stripers were hitting hard) but with a much increased anxiety level!