Mermaid Down

The indie horror film Mermaid Down opens with two fishermen hunting down a mermaid, overcoming her strength to string her up and brutally hack off her tail. But fishermen don't see the rewards of their hunt, because one dies during the struggle, and the other is killed by Dr. Beyer, a psychiatrist who happened to be on his boat nearby, and takes the mermaid for himself.

The mermaid grows human legs, allowing Dr. Beyer to keep her as a "patient" in his mental institution for young women. There the mermaid mingles meets a motley crew of patients and staff who think she's just another patient with delusions. But some of them slowly realize that the mermaid is the real deal and needs to be set free.