In old Scotland, the Kelpie is a treacherous water devil who lurks in lakes and rivers. It usually assumes the shape of a young horse. When a tired traveler stops by a lake to rest or to have a drink, he would see a horse, apparently peacefully grazing. When he mounts the horse, the Kelpie dives into the water and drowns its victim. Occasionally it has helped millers by keeping the mill-wheel going at night.