Mermaid Down (2019)

Storyline:
A mermaid is ripped from the ocean by a fishing crew only to be tortured and to have her tail cut off. A seemingly helpful stranger intervenes, but then locks her away in an institution for mentally disturbed young women, where no one believes she is a mermaid. With no way out, she is forced to count on her survival instincts, and fight for her life at all costs.