I've been quite a few times. Every time I've been the water has been crystal clear. There are always stingrays and other fish which are cool to see in the clear water. The fort is also worth looking at and provides a good view of the island.
Be sure to read their rules of ice chest sizes and just minor stuff like that. My family and I went this past summer and it was really nice. I suggest you pack lite since where they drop you off to the other side of the island could be a good hike with too much stuff. We took and ice chest and some sand toys for my lil girl and that was plenty. They do have restrooms and a small snack shack so ya'll can buy lunch. I suggest riding on the first deck espically coming back in casue they have AC which is quite nice after a long day in the sun.