The Gwragedd Annwn [gwrageth anoon] were the Lake Maidens of Welsh legend. Wales has stories of a great many sinister faerie creatures; the Lake Maidens were not of this type, nor were they like Sirens or Nixies. They were beautiful and sometimes married mortals. Like Mer-people everywhere, they liked to sit along the banks of their watery home and comb their long hair.
One of the earliest tales about Gwragedd Annwn is the story of the Lady of Llyn Fan Fach, a small lake near the Black Mountains in Wales. In the 12th century, a young farm lad from Blaensawde near Mydfai saw and fell in love with a Lake Maiden he watched combing out her long golden hair. He married her, but the lady warned him never to strike her even in jest, for if he struck her three times, she would return to the lake. They lived happily for several years during which she bore three sons. But the man forgot and on three occasions gave her a love-tap. At the last tap, the Lady returned to her mountain lake. However, she frequently came to visit her three sons, teaching them the deep secrets of medicine. These boys became the famous physicians of Mydfai. This skill, handed down to them by their Lake Maiden mother, descended in the family until the bloodline died out in the 19th century.
Psychological Attributes: Gentleness with an inner strength that enables one to walk away from unpleasant situations.
Magical Attributes: Deep secrets of healing and medicine.
Source: Magical Mythical Mystical Beasts by DJ Conway