A 73-year-old woman from Argentina died while snorkeling offshore of Key Largo on Saturday.
Passengers and the captain on board The Dolphin told police Maria Aviani was seen swimming around shortly before she was found floating face-up and barely breathing at 2:50 p.m.
They brought her on board the boat and called for help, starting CPR immediately.
Paramedics transported Aviani to Mariner's Hospital, where she was pronounced dead.
An autopsy will be done to determine the cause of her death.