A shark paid a surprise visit to the waters off Pompano Beach on Monday.
However, marine expert Choy Aming said startled visitors at the West End beach had experienced a lucky encounter and were in no danger.
He said: “It’s such a rare event. It’s pure luck to be able to see a shark inside the reef.”
A video of the shark, shared online, showed the shark pass the swimming platforms on the sandbar off the Pompano Beach Club in Southampton.
Two bathers climbed out of the water on to the platform while the shark passed.
The hotel said the guests seen in the video were part of a family from the United States who have since returned home.
Mr Aming said it was difficult to identify the species of shark from the footage. He said it could have been a hammerhead as one was spotted several times close to shore last summer.
Mr Aming added: “Whether it was a hammerhead or a nurse shark, there is no need to panic.”
He recommended “keeping as calm as possible and keeping an eye on them” if anyone was approached by a shark.
He said: “If you’re genuinely nervous, just head calmly back to shore.
“I do quite the opposite, but if you’ve never seen one in the water, stop, watch, and do everything slowly and deliberately.”
Larry Lamb, one of the owners of the hotel, said the shark’s visit had been brief.
He said: “Our water sports centre spotted it and called me on the radio. I saw it maybe 200 yards offshore.
“It just swam in and then swam out. Perhaps it followed the seaweed in.”