Japan
Volcanic island chain south of Tokyo in the warm Kuroshio current, offering lava reefs, arches, turtles, hammerhead and thresher sharks, and wild dolphin swimming, reachable by ferry or plane.
The Izu Islands are a chain of volcanic islands stretching south from Tokyo Bay, administered by Tokyo and part of Fuji-Hakone-Izu National Park. The main diving islands are Izu Ōshima, Niijima, Shikinejima, Kōzushima, Miyakejima and Hachijōjima. The Kuroshio current brings warm water and tropical species, and summer water temperatures reach the mid-twenties. Diving is mostly from shore entries and small boats run by local dive shops. Hachijōjima offers arches, walls and turtles in clear water. Miyakejima and Izu Ōshima are known for hammerhead sharks, and threshers appear off Ōshima in autumn. Around Mikurajima, scuba diving is not permitted, but a resident pod of wild bottlenose dolphins draws snorkellers. Access is by overnight or jet ferry from Takeshiba Pier in Tokyo, or by plane to several islands. Source: Wikipedia, JNTO, Tokyo Islands, PADI.