Similan Islands National Marine Park

The Similan Islands are a chain of granite islands in the Andaman Sea off Phang Nga province, and they are the anchor of almost every northern Thailand liveaboard. What sets the diving apart is the rock itself: on the islands' western sides, house-sized granite boulders tumble underwater into canyons, arches and swim-throughs at sites like Elephant Head Rock, while the eastern shores shelve into gentler hard-coral reefs and white sand. Marine life ranges from the small to the very large. The boulders and reefs hold Moorish idols, powder blue tang, giant morays and a steady traffic of reef fish and nudibranchs, and the plankton-rich open water to the north brings in the marquee visitors. Reef mantas and, in the right season, whale sharks pass through the outer sites, which is why boats push on from here to Koh Bon, Koh Tachai and Richelieu Rock. The islands lie within Mu Ko Similan National Park, which closes to visitors through the southwest monsoon and reopens for a season that runs roughly from October to May. That protection, and the distance from the mainland, are a large part of why the reefs here have stayed in the shape they are.

Confirmed by our research team, reported by independent divers, or observed nearby via iNaturalist — each entry is labelled with its source.

• Redlip ParrotfishScarus rubroviolaceusReported here · unconfirmed
• Striped SurgeonfishAcanthurus lineatusReported here · unconfirmed
• Orangestripe TriggerfishBalistapus undulatusReported here · unconfirmed
• Manta rayManta rayReported here · unconfirmed
• Blue DragonPteraeolidia semperiReported here · unconfirmed
• Powder Blue TangAcanthurus leucosternonReported here · unconfirmed
• Moorish IdolZanclus cornutusReported here · unconfirmed
• Ocellate PhyllidiaPhyllidia ocellataReported here · unconfirmed
• Giant MorayGymnothorax javanicusReported here · unconfirmed
• Halgerda tessellataReported here · unconfirmed