Richelieu Rock, Koh Bon & Koh Tachai - Thailand’s Top Three Diving Sites

Almost everyone who knows would agree that the three best dive sites in Thailand are the two northernmost islands of the Similan National Marine Park (commonly known as Koh Bon & Koh Tachai) and an undersea pinnacle in the Surin National Marine Park known as Richelieu Rock. While they can all be visited by inexperienced and novice divers, they are better enjoyed safely by divers with experience and the ability to descend below depths of 25 metres.

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Pretty much everyone who has any knowledge and experience will agree that the best diving sites in Thailand are Richelieu Rock as #1, and Koh Bon & Koh Tachai competing for runners’ up spot. All three of these diving sites are located off of the west coast of Thailand, in the Andaman Sea. Koh Bon and Richelieu Rock have topography almost to the surface, but Koh Tachai’s shallowest point is a little deeper. All of them are more suited to experienced divers, and the Advanced (30m.) certification is important to fully enjoy their marine life. However, even divers who are only Open Water certified to 18 metres can enjoy some awesome dives at them all. So, what is so special about these three diving spots far out in the Andaman Sea off of Thailand’s west coast? Well, their distant location means that they are constantly fed by cooler nutrient-rich waters that are not polluted by nearby urban areas. Also, being so far away means that they are only visited by people who want to see their natural beauty, and are therefore less likely to damage it. Isolated in deep tropical water ensures that lots of resident species make these three locations their home, and pelagic marine life visits every day to feed, breed or be cleaned.

Thailand’s Number 1 Dive Site is Richelieu Rock

Location: Richelieu Rock is technically located within the Surin National Marine Park, and this is why divers need to pay an additional park entry fee (currently 500 THB) to visit it, even if already on a Similan liveaboard cruise. The location of Richelieu Rock is nowadays found by buoy markers and/or GPS, but at low tide the captains can see the very tip of Richelieu Rock breaking the surface. It’s between the mainland at the northernmost part of Phang Nga Province and The Surin Islands, nearer than half way to The Surin Islands. A speedboat journey would take at least one hour and 15 minutes to reach there from Khao Lak.

Depth: Divers can enjoy Richelieu Rock at all recreational depths, including right up to the surface. However, entry and exit for divers need to be a little away from The Rock itself, so that the boats don’t damage the reef or their hulls. The bottom of the reef is around 35-40 metres before the seabed slopes away to depths much deeper than normal divers are able to descend to.

Marine Life: Almost everything and anything can be found here. Richelieu Rock is an absolute haven for the multiple species, and treasure trove for divers and predators. Anything from Ornate Ghost Pipefish and Seahorses, to Whale Sharks and Manta Rays are often seen here. Some divers will jump in and expect to see something large and special, and they spend much of their dives gazing out into the blue. However, those who do this will surely miss out on the hundreds of thousands of specimens that either call Richelieu Rock home, or come here to feed, breed or be cleaned. Big, medium and small fish and invertebrates are all found here, as well as marine reptiles including turtles and sea snakes.

Diver Level: Open Water divers certified to 18 metres can enjoy more than one wonderful dive here, but those who are certified to 30 metres will see more. To be honest, divers who have less than 20 logged dives won’t fully appreciate the glory of Richelieu Rock, mainly because they may still be focussing on improving their diving skills to notice how much is going on around them. Even divers with 1,000 or more dives still get excited about Richelieu Rock, such is the colour, teeming marine life and the fact that no two dives are the same here.

Highlights: It’s impossible to pick pout one or two highlights of Richelieu Rock, because there is so much to see, so much going on, and because different divers get excited about different things. Whale Sharks are seen here more often than most other places in Thailand, but they are never guaranteed. There is a yellow Thorny Seahorse at around 32 metres, and an Ornate Ghost Pipefish not far away at around 25 metres. Probably one thing that everyone notices and remembers is the masses and masses of purple soft corals that are all over this dive site. While some people claim that these purple corals’ colour are the reason Richelieu got its name (from Jacques Cousteau, who referred to Cardinal Richelieu), it is more likely that the site was named after the only non-Thai Admiral of the Thai Royal Navy (a Danish man called Andreas du Plessis de Richelieu).

Sea Conditions: Visibility is normally excellent here at Richelieu Rock, but there are times when it is very limited. There is nothing anyone can do to control or predict this. Luckily, if the visibility is poor, there is more than enough small stuff to focus on, so it’s no problem. Due to its location in deep sea and far from any island or the mainland, currents can be an issue. However, the shape of Richelieu Rock means that there’s always somewhere to shelter from any current, and plenty to see all around. 

The Huge Granite Boulders of Koh Tachai Dive Site

Location: Koh Tachai is the northernmost island of the Similan Islands National Marine Park. It is actually nearer to The Surin Islands (34km.) than it is to The Similan Islands (44km.). It’s 48km. from Koh Phra Thong, which is a larger island almost connected to the coast of Phang Nga. Koh Bon is 25km. south of Koh Tachai. Richelieu Rock is about 35km. to the northeast. Koh Tachai has a pristine beach on its north-eastern side, but this was closed to the public in May 2016 until further notice. It may be open again by the time you read this. The pinnacle (dive site) is at the southern end of Koh Tachai.

Depth: The shallowest depth of Koh Tachai is not very near the surface, and divers have to therefore come down the mooring line around 12 metres if there’s a current, and safety stops are done out in the blue. The dive site gets as deep as you want to go, but realistically 30 metres is a sensible maximum depth, and the deepest that nearly all of our dive centres allow guests to descend to anyway.

Marine Life: Almost anything can be seen here, including large pelagic species. The reefs are healthy and diverse, so there is a lot of life in all the nooks and crannies. Skunk Anemonefish/Clownfish are abundant, and there are several different species. Triggerfish are also a common sight. From the smallest to the largest species in the sea, you won’t be disappointed.

Diver Level: This dive site is not really ideal for new or novice divers, nor is it suitable for Scuba Divers and DSD divers, who are limited to 12 metres in depth. Open Water divers with more than 10 dives will do ok here, but really having 50 or more logged dives is necessary to fully enjoy the whole dive site.

Highlights: The huge granite boulders that make up the dive site are something every diver remembers Koh Tachai for. Even without fish, this topography is wonderful to dive around, whether going through swimthroughs or pretending you’re a fighter pilot on Star Wars, the topography is a lot of fun. Add to this the healthy corals, lots of reef life and the chance of a Manta Ray or Whale Shark, and you will soon understand why so many diving professionals see Koh Tachai as their favourite dive site in Thailand.

Sea Conditions: Koh Tachai is infamous for its current. I remember my first ever dive there, I just held onto the mooring line while the others in my group dived around the boulders. I was inexperienced, and hadn’t believed the briefing information that you can easily find shelter from the current between the boulders. Last week (nearly 20 years later) I was there again, and although the tide chart predicted current, there was almost none. This is another thing Koh Tachai is well known for: being unpredictable. Divers should always expect some current, and be prepared for it. Visibility is usually excellent, but can also throw up some unpleasant surprises.

Manta Rays at Koh Bon Dive Site

Location: Koh Bon is about half way between Koh Tachai and Similan Island #9. It is slightly nearer to the mainland than any of the other islands, including Richelieu, Koh Tachai, and all of the Similan Islands #1-#9. However, because Tab Lamu Pier is a little to the south of the nearest point of mainland to Koh Bon, the travelling distance from Tab Lamu to Koh Bon is almost identical to the distance from Tab Lamu to Similans #6-#9. Even by speedboat, any journey from the mainland to Koh Bon will take at least an hour.

Depth: There are two dive sites at Koh Bon. The best and easiest is Koh Bon Ridge, while Koh Bon Pinnacle is only for experienced divers because it starts at 18 metres and is prone to currents. Koh Bon Ridge is shallow enough to snorkel at, but realistically, the diving fun starts at around 8 metres you can go as deep as 30 metres or more, but there’s not much point in doing so. All the action and visibility is better enjoyed shallower than 20 metres.

Marine Life: Koh Bon is famous for its Manta Rays. They are never guaranteed, but especially towards the end of the diving season (March-May) there are more frequent reports of these wonderfully-graceful gentle giants. Even without Manta Ray sightings, Koh Bon is very special, and has lots and lots of interesting creatures, some of which live here and others visit. These include Barracuda, Trevally, and even the occasional Whale Shark.

Diver Level: Although there’s no beach at Koh Bon, there is a shallow bay with plenty of life and easy diving. This means that diving skills can be taught/practised there, and divers who are new, inexperienced or learning can also enjoy some nice diving at Koh Bon. Last week I dived with two large Manta Rays, and the deepest I was at during this time was just 16 metres, so it’s fine for all certified divers. Koh Bon Pinnacle is a different story, though and is only suitable for experienced divers who are certified to 30 metres and willing to jump from the boat and do a ‘Negative Entry’ to ensure a swift descent to the dive site in a current.

Highlights: Manta Rays are the main highlight of Koh Bon, but Whale Shark sightings aren’t unheard of, and there are also lots and lots of other wonderful species. The last time I was there I felt a little sorry for a particular fish that would have been pointed out at any other dive site, but was ignored while we all looked for/at a Manta Ray.

Sea Conditions: The visibility at Koh Bon can range from as little as 10 metres up to more than 30 metres. Don’t worry too much, though because low visibility is often caused by plankton, and Manta Rays & Whale Sharks eat plankton. Also, these filter-feeding giants aren’t scared of calm divers, but they don’t like to be chased by excited divers. Therefore, if the visibility is poor, there may be something special there that you can’t see straight away. And if the visibility is good, you can appreciate these wonderful creatures from further away, without having to disturb them.