A few years ago, I stayed at the Intercontinental Ishigaki Resort and they have a really great snorkeling/diving area right off their beach. We reserved a guided snorkeling tour for two with a private guide who took us by boat to the best area off the beach where we spent about an hour snorkeling and taking photos (the guide also took underwater photos of us). This was reserved through the activities desk of the hotel, but I would imagine that you don't have to be staying at the hotel to make a reservation. It was a really memorable and fun experience, which you can probably arrange just by calling the hotel. They have scuba diving too. https://www.ihg.com/intercontinental...hoteldetail_ic