I visited North Bay on my trip to Andaman. I remember it more for swimming in the clam waters rather than the snorkeling I did for the first time. I somehow liked scuba diving much more than snorkeling hence it took me so much time even to mention snorkeling. Another issue about snorkeling at North Bay in Andamans is that people share the mask, so what you just took in your mouth, a while later someone else is going to do the same. Also before you took it … you get the picture! Not sure how this sharing happens at other places and what are the standards for snorkeling at other places.
At North Bay there are glass bottom boats avail through which you can see corals and fish but for me scuba diving is the best way to see marine life. And those dead corals at North Bay? Well they make a pretty picture.