Northern Dive Sites

Koh Bon

Koh Bon at a Glance

Depth: 10 - 40 m
Currents: Moderate - Strong
Season: Nov. - May

Also called: Koh Bon West Ridge, Koh Talu

Koh Bon is a small isolated granite islet about two hours sail north of the main Similans group. However, Koh Bon is still part of the Similans National Park. Although basically composed of the same rock as the Similans, the landscape above and below the water is very different at Koh Bon. Where the Similans consist of large rounded boulders, Koh Bon is much "sharper". The main dive site, the "West Ridge", is marked by a knife-edge of rock jutting out from the island's western tip. Below the surface, the bottom is littered with giant, almost cubic, boulders.

Currents can be strong here, so this is a good spot for drift diving. But, be careful of your depth, as it's quite easy to go beyond your no decompression limits. Also be sure to check which way the current is running, and make sure your boat will be able to spot you no matter where you surface.

In the various corals, you'll find a wide variety of reef fish, including may kinds of Clownfish, surgeons, Moorish idols and some sweetlips. You will notice a few patches of coral destroyed by dynamite fishing, but this has supposedly stopped, and there's still lots to see.

Manta rays have been known to frequent this area, and it's said that this is the place you're most likely to see them in the Similans. Other large visitors include leopard sharks, whitetip and blacktip reef sharks, as well as nurse sharks.

Koh Bon Pinnacle

Due north of the ridge around 100 meters is a pinnacle that is one of my favorites of the Similans. There are no moorings or other markers on the spot, your boat's captain will have to use his depth-finder to locate the pinnacle, and you'll have to be careful to dive straight down or risk missing it entirely. Given the risks, the pinnacle should only be dived in slack tide. But, there's a very good reward in store for you should you find the rock. It's rather large, although you could conceivably circle it in a single dive. There are several crevices, where you can find fans holding small cowries and ghost pipefish. There are also lots of the ever-friendly batfish around. In a somewhat protected area on top of the pinnacle is a large anemone "garden". There are also almost always some large jacks and trevallies on the hunt as well.

Boats often anchor and spend the night in the relatively protected bay on the southwest side of the island. The bay can make a good night dive, and the snorkeling is even pretty good.

Koh Tachai

Koh Tachai lies about 20 kilometers north of Koh Bon, but is still part of the Similan National Park. The island has a nice long sandy beach on its southeastern coast, with only a park ranger station keeping it from being the perfect desert isle. The island makes a good overnight mooring spot for those making a run up to Richelieu Rock.

However, the island does have a couple of good dive sites of its own. The Tachai Pinnacle, off the southern tip of the island, is a fairly spectacular site in its own right. The reef off the east cost of the island is also a nice end-of-day dive spot.

Leopard Shark Reef

Leopard Shark Reef at a Glance

Depth: 5 - 25 m
Currents: Mild
Season: Nov. - May

Also called: Tachai Reef

Leopard Shark Reef runs along the east side of Tachai Island. It starts very close to shore and extends out around 100 meters or so. The sandy bottom is covered with thick patches of staghorn, fire, brain and other corals, around a few boulders here and there. I did a sunset dive here that was quite enjoyable, and this is a good spot for a night dive as well.

Leopard sharks are a common sight here, hence the common name for the reef, as well as parrotfish, lionfish and moray eels. On a night dive, you may see cuttlefish coming to investigate any lights.

The reef is a common mooring spot for the night, before making a run up to Richelieu Rock.

Tachai Pinnacle

Tachai Pinnacle at a Glance

Depth: 12 - 40 m
Currents: Moderate to Strong
Season: Nov. - May

Also called: Twin Peaks

I have to say, Tachai Pinnacle is not my favorite dive spot. The site is actually a pair of large submerged boulders about 500 meters off the southern tip of Tachai Island. The southern-most pinnacle is the larger of the two and marked by a mooring buoy. The top of the pinnacle is about 12 meters down. The bush coral at the top has been known to hide frogfish, while leopard sharks can often be seen on the sandy bottom around the pinnacle.

The trouble is the pinnacle site is infamous for its strong currents, especially around the full moon and new moon periods. As our dive master said, "The mooring line is your friend." Use the line for descents and safety stops. Use the pinnacles to shield you from the stronger currents, but even that is often not enough to keep you from using up your air all to quickly. There are some large crevices in the rocks, and if you look closely at the fans inside you might find some interesting small critters. The crevices might also help shield you from the currents.

Richelieu Rock

Richelieu Rock at a Glance

Depth: 5 - 40 m
Currents: Moderate to Strong
Season: Nov. - May

Also called: Hin Plo Nam

Without a doubt, it is one of the most famous dive sites in Thailand. The rock lies in open water between the Surin Islands and the mainland. The rock only extends a meter or so above water, and even then only at low tide. Beneath the waves are several more pinnacles, arranged in a roughly crescent shape.

The site is huge, and you could easily spend two or three dives exploring it, and still not see it all. However, as it's in open water, conditions have to be almost perfect to attempt any dive at all on the rock. The pinnacles are covered mostly in soft corals and sea fans. Near the tops of some of the boulders are carpets of anemones.

Of course, what draws most divers to the rock is the possibility, however remote, of seeing a whale shark. But, while keeping an eye out for these giants, don't overlook the small stuff. Look closely and you may find seahorses, harlequin shrimp and ghost pipefish. There are also lots of anemonefish and several species of morays.