The Kerama Islands lie about 40 kilometres west of Naha, accessible by high-speed ferry in 35 minutes or slow ferry in about 70. The four main inhabited islands — Zamami, Aka, Tokashiki, and Geruma — are where Okinawa's reputation for outstanding diving and snorkelling is most fully justified. Visibility of 30 to 50 metres is common; in winter, humpback whales pass through the waters between the islands.
The term "Kerama Blue" was coined by Japanese divers and photographers to describe a specific quality of light underwater around these islands — a clarity and depth of colour caused by the extremely low sediment in the water and the angle of the tropical sun. The phrase has since entered the Japanese travel lexicon as a synonym for the most perfect possible blue sea.
Zamami and Aka are the most visited, each with small villages, bicycle rental, and beaches that are genuinely empty outside of summer weekends. The diving here — coral gardens, sea turtles, reef sharks, and whale shark sightings in season — is considered among the best in Japan. Day trips from Naha are possible and popular; staying overnight gets you the beaches to yourself in the early morning and after the day-trippers leave. Tokashiki is the largest island and has more facilities; Geruma, connected to Aka by a bridge, is the smallest and quietest.