I really enjoy snorkelling. And Okinawa is one of the best places in the world for snorkelling and diving. You can of course drive down to a beach on the main island and snorkel from there. We do that now and again, and it's nice to get into the water on a hot summer day, but with the exception of a few spots the views aren't really spectacular. Instead the best areas are on other, smaller islands. And the closest is the Kerama islands, close enough to Okinawa island that you can clearly see them from the Naha seaside.
You can go there by yourself. Take a ferry to Tokashiki or Zamami, then rent a car or bicycle to get around. Perhaps stay overnight. But you'll spend a lot of time just getting around and looking for good places. Great if you want to explore the islands.
If you don't have that much time to spend, or if you simply want to get to a good spot and snorkel, you can instead book a tour from Naha, and get to a guaranteed good spot in less than thirty minutes for no more money that you'd had spent on ferry and transportation. Also, the tours can take you to spots away from the coast that you just can't reach by yourself, and an organized tour is safer should something happen.
We went on such a tour Saturday two weeks ago. It's pretty relaxed; you get down to the harbour in the morning, get on the boat, and they give you equipment and explain things if you don't have your own mask, snorkel or fins. The boat stops right at the spot, and you get an hour and a half in the water before it's time to return to Naha. We left after breakfast and returned home just in time for a shower and lunch.
Yellow coral just under the water line.
I seem to have attracted an observer.
Yellow coral with some inhabitants.
A closer look.
Many areas are teeming with sealife.
A few other coral species. Some sea anemones too,
but I didn't get a good picture.
Another closeup of the coral.