Koh Tachai, Similan Islands - Thailand Dive Sites

Koh Tachai is one of the Similan Islands’ best dive sites but also one of the most volatile. Massive fans, huge schools of fish, the possibility of manta rays – it’s all to play for.

Barracuda Ball, Koh Tachai, Similan Isalnds, Thailand
Barracuda Ball, Koh Tachai , Similan Islands, November 2024 © [email protected]

A series of pinnacles just off Koh Tachai island, Koh Tachai dive site is one of the best in the Similans – but it can also be quite challenging to dive. The reason being the currents are very volatile here – they can change during the course of a dive seemingly at random.

Ric and the giant fan corals, Koh Tachai, Similan Islands, March 2025 © [email protected]

The reward is that Koh Tachai is a truly dynamic dive site, attracting huge schools of fusiliers, barracuda and batfish which can make it feel like being in a fish bowl. There’s a palpable energy to diving on Koh Tachai.

Barracuda Tornado, Koh Tachai, Similan Islands, Thailand, February 2025 © [email protected]

On one Koh Tachai dive we hit the motherlode – a full on barracuda tornado swirling over the top of the pinnacle in around 10 metres of water. Hundreds of barracuda moving in perfect synchronicity creating a huge spinning cylinder over the dive site. Koh Tachai is that kind of place. (See more barracuda tornado photos).

Fan corals and glassfish, Koh Tachai, Similan Islands, November 2024 © [email protected]

There are also some spectacular large fan corals amongst the big rocks that make up the pinnacles themselves. Very occasionally manta rays are seen here too, but there are resident spiny lobsters and octopus which are much more frequently spotted – if they break cover.

Octopus at Koh Tachai, Similan Islands, October 2023 © [email protected]

Once on the top of the pinnacle at 12 metres it’s fairly easy to stay sheltered as the rocks slope down to 25 metres, provided your dive guide knows their way around the site.

Fan corals and glassfish, Koh Tachai, Similan Islands, January 2022 © Chris Mitchell

There is a second and third pinnacle which you can swim over too if conditions are calm enough. At the second pinnacle there’s some more awesome corals.

Koh Tachai Batfish, Similan Islands, October 2023 © [email protected]

Batfish are also frequently encountered hanging around the main descent line onto the top of the pinnacle, and sometimes in big schools out in the blue. They like to come in and sit over the rocks to get cleaned.

School of sturgeonfish, Koh Tachai, Similan Islands, February 2024 © [email protected]

When Tachai is calmer, schools of humpback snapper and sturgeonfish also sometimes show up as well, and it’s always lovely to see their bright colours amongst what can be quite a murky dive site at times.

Humpback snapper, Koh Tachai, Similan Islands, February 2024 © [email protected]

Not knowing what to expect is part of Koh Tachai’s charm – some dives can be a bust with bad viz, strong currents and not much around – but most of the time, something awesome usually happens. As such, it’s worth putting up with Tachai’s temper tantrums and it repays repeated diving as you get used to the dynamics of the site.

Grouper, Koh Tachai, Similan Islands, Thailand, February 2025 © [email protected]

This is about the only time I’ve ever got a decent photo of a grouper as they always do a runner as soon as they spot divers. They like to hide in amongst the rocks.

Fusilier sphere, Koh Tachai, Similan Islands, November 2024 © [email protected]

Massive schools of fusiliers, thousands of them, also show up every so often and when they do, it’s like it’s raining fish – it gets darker above you as there’s so many fish blocking out the sun, and then they sweep down over the pinnacle and weave around any divers in their way.

Fusilier storm, Koh Tachai , Similan Islands, November 2024 © [email protected]

Forget being able to see your dive buddy – it’s just a blur of blue and yellow until they’ve stampeded past.

Barracuda school breaking up, Koh Tachai, Similan Islands, November 2024 © [email protected]

Even if you don’t get to see a barracuda tornado, there’s usually a big school of them hanging just off the pinnacle out in the blue, often quite shallow. As ever, you need to always be looking.

Pook and the giant fan corals, Koh Tachai, Similan Islands, December 2024 © [email protected]

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