The earliest account is A. W. Moore's, in his Folk-lore of the Isle of Man of 1891. Beside the water bull the Island had a monster called Cabbyl-Ushtey, or water-horse, sometimes called the Glashtin, which Moore compared to the Irish Phooka, who appears sometimes as a bull and sometimes as a horse, and to the Scandinavian Nykr or Vatna-Hestr, the water-horse that lives in salt or fresh water and associates with ordinary cattle. In 1859 it was reported that an animal of this kind was to be seen in a field near Ballure Glen, and hundreds of people left Ramsey to catch a sight of it, but they were doomed to disappointment. The people about Glen Maye believed that the glen below the waterfall was haunted by the spirit of a man who one day met the Glashtin or Cabbyl-Ushtey, and thinking it an ordinary horse got upon its back, when it ran off and disappeared in the sea and the rider was drowned. Moore drew on J. F. Campbell's Highland tales for the wider family: the water-horse who falls in love with a lady and is found out by the sand in his hair when he lays his head on her knee, and who as an old woman sucks the blood of a shieling full of damsels save one who escapes over a burn which he dare not cross, from which Campbell concluded that the old Celts must have had a destroying water-god to whom the horse was sacred.

John Rhys, collecting in 1891, found that what he took to be a kelpie was called by his informants a glashtyn, which Kelly's dictionary defined as a goblin, an imaginary animal that rises out of the water, and that one informant was definite it had nothing human about it but was a sort of grey colt frequenting the banks of lakes at night. In the second volume of his Celtic Folklore he set the Manx glashtyn with the Lowland kelpie and the Norse Nykr, a northern Proteus who takes many forms but prefers that of a grey water-horse, and used the water-horse to explain the kings with horse's ears in Welsh and Irish legend. W. Walter Gill, in 1929, distinguished the Cabbyl Vooar or Big Horse, the sea-going water-horse of the shore, from the grey Glashtyn of the rivers and pools. The Cabbyl Vooar was seen at low tide and towards twilight on the seashore or about the tracks up the cliffs, white like a breaking wave or dun like the rocks, and could travel under the sea as well as over the land, and anyone reckless enough to mount him was carried into and under the tide.

Gill also told the Glen Maye tale as the oldest tale of all, a thousand years old, in the words of his informant. A man walking home from Peel late one night saw a horse standing under the trees at the foot of Raby hill and swung himself onto its back to finish his journey riding. Away it went at a gallop, and as he leaned forward on its neck he was startled to see that its ears were human ears. Knowing by this that something was wrong he threw himself off in the nick of time, for the horse leapt the hedge and bolted for the river, and the rider escaped drowning at the cost of a broken leg. Gill knew the story of a girl seized by the water-demon and escaping by cutting off a piece of her dress at Glen Maye, Colby Glen, Sulby and Ballure, and he set the Lonan Nikkesen of the Awin Ruy pool among the same creatures, a drowner of girls whose name came from the Norse, and whose tradition, he added, did not originate in the Isle of Man.