Off the west coast of Okinawa in the East China Sea, the snorkeling at Kume Island is popular for observing clownfish. Offshore of Kume Island is a large shoes. The Hatenohama Sector of the shoal offers the best coral and marine life for snorkeling.
The snorkeling off Okinawa is best from May through October when the water temperature is more enjoyable for snorkelers. However, that is also the prime time for the stinging Habo Jellyfish, which is a type of box jellyfish. Since 2012, the local authorities have been posting more snorkeling restrictions/prohibitions at Okinawa beaches, so make sure to look for signs and follow them to avoid being arrested.
To reach the snorkeling in Okinawa by air, you will need to fly into Okinawa Naha Airport (OKA) on southern end of island. Then from Naha, there are public ferry boats that head west over to Kume Island.
Overall, Kume Island is the 12th most popular snorkel dive spot of all 12 snorkeling dives in Japan.