The Chief Fun Officer @Holly and I went down to the Florida Keys following Hurricane Irma and were the first people to snorkel from John Pennekamp when it reopened.
The water was a brilliant turquoise on the journey out, with plenty to see among the mangroves on both the outbound and return journey.
But the real gem of the experience was the snorkelling, with plenty of fish and coral to see.
In particular gorgonians (fan coral, among others) and the variety of tang/surgeon fish. The reef around the Keys is part of the Great Florida Reef and is part of the third largest barrier reef on the planet.
Some people also call it the Keys Reef Tract or other combinations of "reef" and "great".
We snorkelled the Grecian Garden, one of the more popular spots for seeing fish and coral. Another popular spot features a sunken statue of Christ the Redeemer. Note that your captain will be the one to call your "dive" spot based on water conditions and how busy it might be on the day.