The difficulty in defining the kelpy in comparison to related beings, such as the water-horse, is a similar challenge that faces those who would comprehend the nature of the blue men.
t]here is hardly a district without some legend of a Linne na Baobh (Badhbh): very often the water-horse is represented as a kind of creature covered all over with rags and ribbons, typifying the wind-tossed surface of the waves.
The supernatural threats that inhabit the waters of Scotland comprise a veritable bestiary: assorted fairies, glaistigs, dragons, water-bulls, water-horses, kelpies, selkies, blue men, and mermaids.
More ambiguous than the threat of sea-hags, mermaids, and dragons is the nature of glaistigs, water-bulls, water-horses, and kelpies.
Unlike glaistigs, water-horses would not willingly perform service to a household; encounters with water-horses were always considered dangerous.