I would pick something else.
We went in march, the water had brown algae floating in it. It is a large lagoon, but all the fish are under a fish feeding station and will not leave forfear they may miss a bit of food. You can catch and hold a yearling turtle, which was cool. There is an aviary there, and they also have the famous blue iguana, native to only the cayman islands. We went there to see the the iquana and to snorkel figuring that we could do both. The snorkeling was horrible, but the rest of the park was clean. If we could do it over again, we would do one of the snorkeling charters. Good luck with what ever you decide.
Wow, I'm amazed that they're letting it go like that! When we were there last year, the water was clean and the fish were everywhere...great snorkeling. All of the facilities were extremely clean, including the showers (which I am very fussy about), and I was looking forward to returning in Jan.