Lorelei
One of the most beautiful water spirits ever known - Lorelei was a German girl who was unlucky and love and so drowned herself.
She can be seen sitting on the banks of the Rhine strumming a wistful song on her harp, rather like South European Merfolk or Sirens.
It is said that those who see her lose their minds, or their sight, or both, and others say that she lures sailors and fishermen to their dooms in revenge against her lover.