When a Carribean Island is engulfed by a revolution, one unscrupulous American mobster, Renzo Capeto plans to clean up with a get-rich-quick scheme. His diabolical plan is to provide refuge for the loyalists, and the contents of the government coffers, on his boat. He would then murder his passenger and escape with a fortune. Planning to blame their deaths on a mythical sea monster, no one is more surprised than Renzo, when the real monster appears with its own agenda.
You can stream Creature from the Haunted Sea (1961) free and legally on OldReel, via the Internet Archive.
Yes — it is in the public domain and can be watched and shared freely.