A Kelpie is a species, appearing in the Wardstone Chronicles.
The Kelpie is a type of malevolent daemon that has a great hunger for human flesh.
It's a shape-shifter that usually takes the form of a black horse or pony. It allows a human on ride on its back before galloping into the water and drown him.
If particulary hungry, it may bite of the feet of its victim.
Kelpies can be found in rivers and lakes - they are mainly water based.