Forbidden Island is a 1959 American adventure crime film directed by Charles B. Griffith starring Jon Hall. It was his debut as director, although he had directed second unit on Attack of the Crab Monsters. A young Don Preston from the Mothers of Invention appeared in this film.

A freelance frogman (Jon Hall) is hired by a psychotic treasure hunter to recover an emerald that went down in a shipwreck.

https://en.wikipedia.org/wiki/Forbidden_Island