I didn’t dive there but there is good snorkeling on the artificial reef of seven mile beach, if you bring out cereal fish will swarm you for food! Stingray city is also a must see, very awesome!
Here are some good snorkeling spots, that offer different reefs and fish. My favorite was Cemetery beach. I dove with Ocean frontiers and had a blast on the east side of the island. Depending on where you're staying, I would recommend to dive the USS Kittiwake wreck that everyone raves about and a couple of local reefs. Just use tripadvisor to find a dive shop that's close to you, but search around and email the dive shops for any package deals/sites. I would recommend doing the rum tour, but bring a DD since there is no limit on the booze .