A Kelpie is a water demon native to Britain and Ireland. Able to take any form, they usually take the form of a horse with a bullrush mane. After luring unwary travellers onto their backs, they drag them underwater and eat them, allowing the entrails to float to the surface of the water. A Kelpie can be rendered docile and harmless by using a Placement Charm to put a bridle over the the creature's head.
The largest reported Kelpie is the Loch Ness Monster, who resides in Loch Ness, Scotland.