Scottish tradition distinguishes the water horses by water. The kelpie belongs to rivers and burns, while the each uisge belongs to sea lochs and is the more dangerous of the two. Both appear as a fine horse standing conveniently near the water, and both have the same trick: a rider who mounts finds the hide will not release the hands, and is carried under.
Read as a warning, the story is precisely engineered. It puts the danger at the water's edge, it targets the moment of temptation rather than the water itself, and it explains a drowned body found with no obvious cause. Highland accounts often add that the liver is left on the shore, which is the sort of gruesome specific that a story invents to be remembered by children. Tellings in which the kelpie appears as a man, recognisable by weed in the hair, extend the same warning to a different risk.
The name is now attached to two thirty metre steel horse heads at Falkirk, designed by the sculptor Andy Scott and completed in 2013, which stand beside a canal and draw several hundred thousand visitors a year. They commemorate the working horses of Scottish industry as much as the folklore. It is an unusual afterlife for a drowning warning, and for many people now it is the first meaning of the word.