It's pretty singular that this exists because "mermaid" is my monster of choice when discussing innovative villains with friends. Mermaids, before they were little mermaids and dolls with brushable hair, were the Sirens of The Odyssey and objects of simultaneous desire and terror. Sounds good to me. SHE CREATURE is pretty close to what I had in mind and the fact that is works so well is a credit to me and my good ideas.
Some Irish carnies with a mermaid act get a real mermaid through carny chicanery and plop her on a boat for the States, where money can be made. One of the carnies is a relatively sweet and sympathetic character named Lily, who becomes frienemies with the fishwoman. Also, mermaids have a sort of problem once a month or so with their weird moon cycle business. That is plenty of plot to make a good movie.
And this is a good movie. I cannot believe it was made for television (IMDB says), because the performances and direction and atmosphere are far too professional. IMDB also says that it's "Mermaid Chronicles Part I", although I wouldn't bet on a sequel appearing ten years after the fact for a movie that almost no one has ever heard of. Unless you make it happen, horror consumer.
Thankfully, this is a very self-contained story and it's enjoyable as a self-contained thing, although it definitely leaves space open for future killer-mermaid adventures. I wasn't going to hate any movie that had both carnies and mermaids, but I didn't expect to love this as much as I did. Recommended as hell.