[6] It was believed to be a spirit assuming the shape of a horse, usually grey or black with a white mane, sometimes glowing or winged, to entice unwary travellers to ride him.
The water-horse of the River Honddu, specifically, had a "tormenting" reputation, as shown by a story in which it carried a weary man from an ancient Roman camp near the town of Brecon to the banks of the Towy, not far from Carmarthen.
Three days later it carried him back, but "in a worse state than when he left, for the ceffyl dŵr had dragged him through mire and water, through brambles and briars, until he was scarcely knowable".
[6] Despite the general association with rivers and waterfalls, the ceffyl dŵr was often seen on seashores, where he was described to be either dapple-grey or sand-like in colour and could be recognised by his hooves being turned the wrong way.
It's described as a miniature horse with a black coat and a white mane which, despite its small stature, carries the protagonist through the air across a vast distance before vanishing and leaving him there.
There is a tale of a parson and parish clerk walking home from Cardiff one night in the 18th century when they found a horse and, believing it to be a stray, decided to ride it to quicken their journey.
[6][3] A similar story comes from Lydmoor, which tells of a travelling minister who, when pausing for rest beside a stream, was joined by a deacon of Trehill Calvinistic Methodist Chapel.