Dwynwen was a beautiful fifth century Welsh princess (sounds miraculous already, right?) who felt dreadfully sorry that a handsome man named Maelon was in love with her. Oh, she liked him fine, but she had already pledged to remain a virgin. She prayed devoutly that he and all lovers might find true and lasting love, but not with her.
The well at her tidal island nunnery became a wishing well, especially for young lovers. Young women would scatter bread crumbs on the surface, and then place their handkerchiefs over the crumbs. If an eel rose and disturbed the surface, their husbands would be faithful. I might say something, but it hardly seems necessary.