In olden times, water horses used to sport in the Welsh countryside, people tell. Common people may still be afraid of the power of the water horse, and swimmers are on their guard against his attacks, for he chokes and carries off under water those he catches. Therefore ferry-men warn those who are crossing dangerous places in some rivers not so much as to mention his name. If not there might rise a storm and they could be in danger of drowning.
The spirit who delighted to take on the form of such a dark horse, dashed with its riders through briar and brake, through flood and fall, over mountain, valley, moor, and river. Sometimes he took on the form of some other animal and leaped on the shoulders of the unwary traveller. But the weird clergy rode the water-horse without danger, and could sing: "I am a merry wanderer of the night. Black are my clothes. I can ride on while sleeping, without harm."
It was believed that they could conjure up the River Horse by shaking a magic bridle over the pool he lived in.
A man caught a long-haired mermaid and took her home to his house, but she did nothing but beg and beg to be allowed to return to the sea. The man did not heed her entreaties, but kept her enough in a room and fastened the door so that she could not escape.
She stayed there several days, beseeching the man to release her, and then she died. Afterwards a curse seemed to rest on the man, for he died miserably poor.
Also, on Isle of Man some persons captured a mermaid. They carried her to a house and treated her tenderly, but she refused meat and drink and would not speak when addressed. After three days, when she began to look ill, they opened the door, and she glided swiftly to the sea side in a mist. The captors followed her at a distance and saw her plunge into the sea, where she was met by a great number of her own species.
One of them asked her what she had seen among those on land, and she answered with her long hair flowing around her, "Nothing essential and thoroughly accomplished, regrettably. And what they did to me, cannot be to their credit either."