The Green Rock dive site, Koh Tao, is an adventure within an adventure. This isolated granite formation off Thailand’s diving island is riddled with natural swim-throughs — tunnels and passages in the rock that have made the Green Rock dive site legendary among experienced divers. Moreover, it is triggerfish territory: both the titan and the margin triggerfish call this site home, and both will defend their nests aggressively against any intruder who comes too close. A thrilling dive, recommended for divers with solid underwater experience beyond Open Water level.
Min. depth
Max. depth
Boat ride
Trigger pit
Fun dive
Multiple swim-throughs
Trigger pit
Titan & margin triggerfish
Green Rock dive site Koh Tao: the swim-through specialist
The Green Rock dive site is a granite formation sitting off the west coast of Koh Tao, 30 minutes by boat from Mae Haad pier. Its defining feature is a rock structure riddled with natural swim-throughs — passages, tunnels and openings that divers navigate through, creating a labyrinthine underwater experience unlike any other site on Thailand’s diving island. It is precisely this architecture that has built Green Rock’s reputation among experienced divers.
Unlike open-water sites such as Chumphon Pinnacle, the Green Rock dive site rewards exploration of the rock itself. Slipping through passages, discovering what lies behind each wall, and finding the varied reef life that has made every crevice its home. Furthermore, the site hosts an impressive array of reef species: giant groupers, filefish, sergeant majors, butterflyfish and angelfish populate every surface of the rock. But it is above all for its triggerfish that this site has become legendary on Koh Tao.
The Trigger Pit — triggerfish territory at the Green Rock dive site
At the base of Green Rock, between 16 and 25 metres depth, lies a wide sandy expanse dotted with dozens of craters dug into the seafloor: this is the Trigger Pit. Each crater is a triggerfish nest — belonging to either the titan triggerfish (Balistoides viridescens) or the margin triggerfish (Pseudobalistes flavimarginatus). Both species are among the most territorial fish in tropical seas.
During nesting season, triggerfish defend a cone-shaped territory that extends upward toward the surface, which means a diver passing above a nest can be charged even from a distance. Their powerful jaws can deliver a genuinely painful bite. As a result, Green Rock is reserved for divers with solid experience beyond Open Water level, capable of managing an unexpected situation calmly underwater.
If a triggerfish locks eyes on you and starts circling, swim away laterally — never upward, which would bring you further into its defensive cone. The Divers Boat dive guides give a full safety briefing on triggerfish behaviour before every dive at Green Rock. Handled correctly, the Trigger Pit is one of the most fascinating diving experiences on Koh Tao.
Marine life: what you’ll encounter here
Beyond the triggerfish, Green Rock hosts a colourful and varied reef community. Thanks to the richness of the swim-throughs and rocky walls, every dive reveals its own discoveries depending on which depths and passages you explore. Indeed, no two dives here are identical.
- Titan triggerfish (trigger pit)
- Margin triggerfish (trigger pit)
- Giant groupers
- Filefish
- Sergeant major fish
- Butterflyfish
- Angelfish
- Multiple natural swim-throughs
What level do you need for the Green Rock dive site?
The Green Rock dive site is reserved for divers with solid experience beyond Open Water level. The combination of swim-throughs, the Trigger Pit and the potentially aggressive behaviour of the triggerfish demands good buoyancy control and enough underwater experience to manage unexpected situations calmly. Advanced Open Water (AOW) certified divers will be most comfortable here. However, an Open Water certification is the baseline — ask our team to assess your experience level before booking.
Furthermore, Green Rock is an excellent environment for a Peak Performance Buoyancy specialty course. Precise buoyancy control is essential for navigating the swim-throughs without disturbing the corals. Moreover, you can check our diving prices Koh Tao for all available fun dive options.
Dive the Green Rock dive site with The Divers Boat
The Divers Boat organises fun dive trips to Green Rock from Koh Tao, departing from Mae Haad, the main pier on Thailand’s diving island. The journey takes approximately 30 minutes. Our multilingual dive guides give a full site briefing before every dive — including specific guidance on triggerfish behaviour and how to navigate the swim-throughs safely. In addition, Green Rock pairs naturally with other west coast sites such as Sail Rock for a varied and memorable dive day.
Contact our team to book your dive and ensure a properly guided, safe experience at this one-of-a-kind site.
Book your fun dive with The Divers Boat — SSI dive centre at Mae Haad, Koh Tao.