In the early scene with Steve Singleton and Katherine Shelley swimming off his schooner, John Payne has a deep, dark tan. But in the next scene when Jumbo Johnson meets up with them, Payne has hardly any tan at all. And, while he is slightly tanned in succeeding scenes, he's never as dark as in the beginning.
Although the story takes place is several locations, every time the characters are seen underwater, they are swimming in exactly the same place, with the same underwater growth, rocks, and sea shells.