Japan's largest coral reef, a 20km lagoon with over 360 coral species, giant clams, turtles and shallow gardens you can snorkel…Japan's largest coral reef, a 20km lagoon with over 360 coral species, giant clams, turtles and shallow gardens you can snorkel for hours. Also the front line of Japan's coral crisis, with visible bleaching scars and large-scale restoration plots you can see underwater. Surveyed since the 1970s and protected within Iriomote-Ishigaki National Park. Sekisei lost an estimated 70% of its coral in the 2016 bleaching event, triggering Japan's biggest coral restoration programme, transplant nurseries are now part of the seascape and worth showing honestly. Anchorage: Anchor on sand inside the lagoon, never on coral. Shallow and intricate; good light and a bow watch. Hazards: Coral bommies throughout, eyeball navigation. Box jellyfish in summer. Typhoons Jul-Oct. Plus