"Ondine" Movie Spoiler: The girl the fisherman finds in his net appears to be a selkie--a seal that becomes human by shedding its skin. But it turns out she has history--she was carrying drugs and ended up in the sea. But the idea that she is not human is too much for poor Syracuse (Colin Farrell). In the end, she is accepted as human and not selkie so everyone can get on with their lives.
But then the events in the plot, namely, that she can call fish for him to catch can not then be accounted for. No one is that lucky and the movie is not about luck. The events in the plot indicate she is a mermaid who revives the drowned body of a human woman and then (exactly like real mermaid women) she lives among us disguising who she really is. But the movie never touches this possibility.