Koh Tachai is an amazing island to visit for diving. It is the most Northern island in the Similan National Marine Park. It is an island on its own in the open sea that has some different dive sites on offer. Divers and snorkellers tend to dive on one side of the island; there is more to see on this side.
Koh Tachai Reef
There is a lovely beautiful sloping reef next to the island that can go down to around 25-28m where the reef ends and the sand begins. Now there is still a lot to see down there in the sand, kuhl’s stingray, jenkins whipray, garden eels, passing tuna, trevallies, barracuda and much more.
The slope itself is full of hard coral, where you can see a huge variety of small to medium sized fish, lots of crustaceans and hunting trevally and emperors, this also makes it a nice place for a night dive, where you can start on the sloping reef and end within the shallows.
The shallow part of the dive site is broken up a bit more, so you will swim in between coral bommies and sand. If you stay super shallow (somewhere between 3-5m) you might be lucky enough to see some blacktip reef sharks and turtles. This is a very popular place for the sharks, they like to stay shallow and move in between the rocks and coral but they are very shy of divers, so they won’t get too close and you’ll most likely see them swimming past you, it’s not often that they hang around.
Koh Tachai Dome
Just off the Koh Tachai island, there is a pinnacle in the sea and this is the main dive site that has many names; Koh Tachai Pinnacle, The Dome, The Dome of Doom. The site sits away from the island it is exposed to current, which is what makes this site unique.
In the middle of the site there is a big rock shaped like a dome, where the top of rock sits at around 13-15m and around it consists of smaller rocks that lead off to the sand which can get as deep as 30-35m. This site can be exposed to some strong currents, so on some dives you will have to use those smaller rocks as protection, but because of these currents you will be able to see some stunning marine life. Normally gorgonian sea fans grow one way, but here you will see that they have grown in several different directions due to the currents. Surrounding the site you will see bluefin and giant trevally, and sometimes you will see the tornado of barracudas. If you look down in the corals and rocks you will see some tiny nudibranchs and flatworms. If you’re really lucky you might see the big stuff swimming by, whale sharks and mantas.
There is also a second pinnacle that you can swim out to if the conditions allow. This is on the North side of the first pinnacle. You can follow the rocks out and you will eventually find it. During the swim across you may encounter some sharks. The bottom of this pinnacle sits around 27m and the top at 14m.
SCUBA Level: Beginner – Advanced
Temperature: 27-30°C/81-86°F
Visability: 10-30 m/33-100ft
Depth: 3-25 m/10-82ft
SCUBA Level: Medium – Advanced
Temperature: 27-30°C/81-86°F
Visability: 10-30 m/33-100ft
Depth: 13-35 m/10-82ft
What to watch out for
Koh Tachai Dome is renowned for having current, however you might go there and not experience any. But there is a famous current that runs through the Similans called ‘The Green Monster’, and it often flows through Tachai. The Green Monster is easy to spot coming towards you, it’s green! Once it hits you, you will feel the temperature drop a few degrees, the visibility is reduced and it’s current, so you may need to drift with it or swim into it (depending on how strong it is). But once it has passed you’re left with a crowd of many fish. But this is why Koh Tachai gets the megafauna – because of the currents.