The Scottish water horse said to devour those who ride it is the each-uisge.
The each-uisge is a dangerous shapeshifting water spirit of Scottish Highland folklore. Its name literally means “water horse.” It is commonly imagined as a beautiful horse waiting near a loch, but it may also appear as a handsome man or a huge bird. An unsuspecting rider who mounts the creature becomes stuck to its adhesive skin.
The each-uisge is said to carry its victim into deep water, drown them and tear apart the body, leaving the liver floating to the surface. Folklore also gives it a taste for cattle, sheep and human beings. Sea lochs and freshwater lochs are its usual habitats, while the related kelpie is more often associated with rivers and streams.
The creature is not exclusively Scottish: Irish folklore has the related each-uisce, often anglicised as aughisky, and Manx tradition has the cabbyl-ushtey. Ceffyl Dŵr is Welsh, Nuckelavee is a different Orcadian monster, and a kelpie is a related but distinct water spirit.