Thats the island where Gilligan's Island was supposedly filmed.
The cruise ships sell trips to it. You can go there easily on the water taxi ... about a 20 minute ride. Once on the island you can buy sodas, beer, sandwich, etc.
Go early in the morning as possible to begin detecting under the many hammocks scattered around the area before they get "saved" by people putting their stuff on them. Lots of lost coins and jewelry dropped from the hammocks into the deep soft sand under them.
Later in the morning, work the water in the area where the little bridge crosses over to the far side of the lagoon. I did better there with finding jewelry than down further in the lagoon nearer where the water taxi docks. Didn't detect there as much due to lots of kids being in that area. Were it fairly clear of folks, it would be worth a try.
That lagoon stays "pond calm" regardless of the wind.
The Atlantis has a beautiful beach right behind it. If wind / tide conditions are right you may find it calm enough to water detect there.
If you are into 3 card poker, play a few hands for me. Have fun.