Scientists are puzzled by dozens of mysterious holes on the floor of Lake Michigan, first discovered two years ago by the Wisconsin Shipwreck Coast Maritime Sanctuary. Despite a recent survey with a submersible robot, the origins of these deep-water craters remain unclear. Maritime archaeologist Russ Green noted the holes were previously unknown. Local shipwreck hunter Brendon Baillod also found similar craters, measuring 20 to 40 feet deep, while searching for a wrecked freighter.