Koh Tachai Similan National Park

Koh Tachai within the Similan National Park is an advanced dive destination centered on one of the most beautiful and remote islands in the archipelago. The island itself, with its pristine white sand beach and dense tropical forest, was once open to overnight visitors but is now restricted to protect its fragile ecosystems, and the diving around its shores reflects this same wild, unspoiled quality that makes Koh Tachai a jewel of the Andaman Sea. The diving at Koh Tachai encompasses multiple sites around the island, with the underwater terrain ranging from gentle coral gardens to dramatic boulder fields and exposed pinnacles. The advanced rating reflects the currents that can be significant around the island, particularly at the more exposed sites, and the depths accessible along the deeper reef slopes and at the famous nearby pinnacle. The coral reefs around Koh Tachai are in outstanding condition, benefiting from the island's protected status and limited human access. Hard coral gardens display exceptional diversity, with table corals, staghorn thickets, and massive boulder corals creating complex reef architecture. The reefs on the sheltered eastern side tend to offer calmer conditions and shallower profiles, while the western exposure presents more dramatic topography with larger boulders and steeper drop-offs. Marine life around the island is abundant and varied. The nutrient-rich waters attract large schools of fish that create some of the most impressive aggregations in the Similan chain. Trevally hunt in coordinated packs, their attacks on baitfish creating explosive surface activity visible from the dive boat. Barracuda form dense schools, and reef sharks patrol the deeper edges. The island's remote position increases the likelihood of pelagic encounters, with manta rays and whale sharks both possible. The granite boulders that characterize the Similan Islands are particularly impressive around Koh Tachai. These massive rounded rocks, smoothed by millennia of wave action, create underwater landscapes of surreal beauty. Swim-throughs between the boulders offer atmospheric passages where light plays through gaps in the rock, and the surfaces of the boulders support rich communities of soft corals, anemones, and encrusting organisms. Koh Tachai is accessed as part of multi-day liveaboard itineraries through the Similan and Surin Islands. The diving season runs from October through May, and the island's position at the northern end of the Similan chain means it is often combined with visits to Richelieu Rock and the Surin Islands for a comprehensive northern Andaman Sea experience. Koh Tachai offers advanced divers the chance to experience the Similan Islands at their most wild and pristine. The combination of world-class reef health, dramatic underwater scenery, and the possibility of extraordinary pelagic encounters makes this remote island one of Thailand's most rewarding dive destinations.