We did this excursion on our August 8th cruise.
The excursion begins with the group being escorted from the pier across the street and through the mall (seems circuitous, but it is the only way) to an open air bus. The bus takes everybody to the southern tip of the island to the eco-park where drove on a dirt rode next to the protected shoreline where we could see the turtle nests and the tracks of the turtles on the sand. We then stopped at the crocodile lagoon where we saw iguanas and a large crocodile. There was a somewhat rickety-looking observation tower that I climbed up to view the lagoon as well. Lots of water birds around too. There was a small mayan ruin here as well. Next stop was at the lighthouse. The lighthouse has a very narrow staircase of 125 stairs to the top. The view was nice. The last few flights had very low clearance and I almost had to get onto my hands and knees to get through the small (maybe 3' tall doorway) at the top. Going down while others were going up (or visa versa) was not fun. There we a lot of jeeps and dune buggies parked here as well...assuming for other tours. Lastly, we traveled to the beach where there was a nice facility....bathrooms, showers, small gift shop, bar, snorkel hut.
Our tour guide had us get our snorkel gear and after a brief safety talk we headed quite a ways up the beach where we entered the water, swam out maybe 200 yards to the reef which we snorkeled along for maybe 500 yards and then we swam back to the beach. The snorkeling was easy for me, but a lot of people had problems. I think some of the children weren't 8 years old and I saw one mother have a heck of a time swimming back against the current with her two small kids in tow. We saw a spotted ray, several hawksbill turtles, some coral on the reef, and quite a few fish. We probably were on top of the reef for 20 mins. The water was very clear. The walk back to our starting point was very long, hot, and tiring.
Water and soda was provided on the bus and at the beach. I didn't see any food available (but I wasn't looking either).
Overall we were pleased with the excursion. We wished there had been food, but that would have made it even longer.....
The beach had quite a steep entry and the water got deep quickly...waist deep within a few feet. The sand was nice, but I wouldn't think it would be the best for small children.