The Similan Islands

Similan comes from the Yawi word for nine, which is how many islands the archipelago originally counted. The park now runs to eleven, numbered from south to north — Ko Huyong is Island 1, Ko Tachai is Island 11 — and the dive sites are still usually given by island number rather than name. Mu Ko Similan National Park was declared in 1982.

The islands are granite, not limestone, and that single fact shapes every dive. The west sides face the open Andaman Sea and are piles of enormous rounded boulders, stacked into swim-throughs, arches and canyons: Elephant Head Rock, Deep Six, West of Eden, Boulder City. The east sides are sheltered and shelve gently into hard-coral gardens over white sand: Anita's Reef, Breakfast Bend, the Moorings anchorages. You can dive both in a day and think you are in two different places.

The park has been under pressure for two decades — the 2004 tsunami, mass coral bleaching in 2010, and simple volume, with five to six thousand visitors a day in high season. Ko Tachai was closed indefinitely in 2016. In October 2018 a daily cap of 3 850 visitors came in, all overnight accommodation on the islands was removed, and liveaboards were no longer allowed to keep guests aboard inside the park. The park also closes entirely from mid-May to mid-October for the monsoon.