Large portions of the (originally Italian) script were actually written on location in Mexico by actor Michael Forest. He was pushed into the role of re-translating (and rewriting) much of it after their original translator (who was Russian) turned them in an English version that didn't make any sense.
Mike Di Donato's mask is a Technisub Bella.
An early movie to feature parasailing, and with more use than merely having fun: They use it for spotting sharks.
The plot, or main destination/goal, of seeking a treasure that's "guarded" by killer sharks is more liken to Cornel Wilde's Sharks' Treasure than Jaws. Wilde's movie came out the same year as Jaws, so it was, for the most part, its own thing.
Future Mexican star Jorge Reynoso, playing a small part as a henchman, is not listed in the Italian version cast list, but is in the Mexican version.