Koh Bon stands apart from the other Similan islands with its unique composition of limestone, not granite boulders, which makes this island distinctive in the Similans National Marine Park. The island also features a hole that runs through it, so if you’re seated in the bay, you can see through to the other side. Near the hole, there is a smaller gap, but you cannot see through this one; water comes through and creates a small waterfall when the waves hit the island at the right time. While Koh Bon lacks sandy shores for sunbathing, its main attraction lies beneath the surface, beckoning snorkellers and divers to explore its underwater treasures. Despite its modest size, Koh Bon offers an array of dive sites, each promising a unique and unforgettable experience.
Koh Bon West Ridge
West Ridge is the most popular of all the sites here. The dive site has everything—a reef, a wall, and a ridge! What more could you want? You can start your dive on the reef, which begins at around 8m. From here, you swim a little and then reach the wall. The wall starts at 5m and descends all the way down to 20-25m; some guides prefer to start their dive along the wall. The wall, made of limestone (resembling jagged layers of rock), continues underwater, providing numerous crevices to explore. The next stop is the ridge; it slopes down and quickly reaches depths beyond recreational diver limits. Unfortunately, at some point, you’ll have to ascend over the ridge or turn back.
The highlight of West Ridge is its role as a cleaning station for majestic manta rays. There isn’t a right or wrong time to visit here; they turn up when they want. As long as you don’t chase them, they will stay. As part of the mobula family, when they swim through the water, it looks like they are flying. Both reef and oceanic mantas come to visit West Ridge.
Koh Bon North Ridge
North Ridge has very similar topography to West Ridge, but it sits on the north side of the island. On this side, there is a gradual sloping reef that reaches sand around 27m. The main feature of the dive site is a ridge extending from the reef out into the open. The ridge extends into the sand, with the rocks at the end reaching depths of 33-35m, covered in white, yellow, and pink soft coral. It’s advisable to carry a torch on this dive to see the vibrant colours of the coral and check the cracks in the rock for small creatures. After exploring the ridge, divers can venture into the sand to spot sharks or jenkins whiprays, return to the reef and head to West Ridge, or head east to the other side of the island. However, caution is needed on the return journey, as strong currents can make it challenging for divers to return to the reef.
Many years ago, this area was popular for dynamite fishing (until it was made illegal), so unfortunately, the coral here is fragmented and scattered on the seabed. The coral in shallower areas tends to be healthier and more abundant. Nonetheless, there is plenty of marine life to observe during your dive, including banded sea snakes, octopus, barracuda, guitarfish, sharks, jenkins whiprays, tuna, and much more.
Koh Bon South Side
Koh Bon South Side differs slightly from the other sites; there are fewer rocks and less coral, but it offers an exhilarating drift dive experience. Starting at the southern tip of the island, there is a small drop halfway through the dive where huge groups of yellow snappers can be seen. As the dive shallows, surprises abound; divers have the chance to encounter sharks, barracuda, peacock mantis shrimp, and octopus. The topography in the shallows is not to be overlooked; diving here at the right time can yield stunning wide-angle photographs under the sun’s rays. Few boats or divers venture to the South Side initially, but as you explore further around the island, its worth becomes evident.
Koh Bon Bay
Nestled in the heart of the island, Koh Bon Bay offers an accessible dive site suitable for both beginners and seasoned divers alike. The bay starts at around 5-6m and descends to 20-25m. This steady sloping reef is adorned with hard coral and teeming with small to medium-sized fish. Further out into the sand, divers will encounter coral bommies that are home to dancer and boxer shrimp. Trevallies and emperors hunt small glass fish along the slope, where huge schools of tuna and yellow back fusiliers can often be seen. Currents may be experienced in deeper areas, but once back in the shallows, the water calms for a relaxing dive. This site is ideal for beginners or divers returning to the water after a break.
Koh Bon Pinnacle/ Hin Luang
This dive site is located on the north side of the island and features a pinnacle in the open sea, where divers may experience currents. The pinnacle’s top sits at 18m, with one side sloping down to around 35-40m and the other deeper side to 50-60m. This relatively small site should be explored slowly to fully appreciate its beauty. The rocks here attract a variety of marine life, including marble stingrays, guitarfish, eagle rays passing by, and occasionally sharks. Returning to the main pinnacle can sometimes require swimming against the current.
In Thai, “Hin Luang” means ‘Yellow Rock’, a name derived from the abundant yellow soft coral that adorns the rocks. Despite its location further out, this pinnacle attracts numerous fish species. Looking into the blue, divers have a good chance of spotting large schools of fusiliers, passing tuna, and barracuda tornadoes. On the rocks themselves, sightings may include red-toothed triggerfish, coral hind groupers, long-nosed butterflyfish, blue-ringed angelfish, and much more.
SCUBA Level: Medium – Advanced
Temperature: 27-30°C/81-86°F
Visibility: 15-30 m/49-100 ft
Depth: 5-40+ m/16-130+ ft
SCUBA Level: Medium – Advanced
Temperature: 27-30°C/81-86°F
Visibility: 15-30 m/49-100 ft
Depth: 8-35 m/26-115 ft
SCUBA Level: Beginner – Advanced
Temperature: 27-30°C/81-86°F
Visibility: 10-30 m/33-100 ft
Depth: 5-35 m/10-82 ft
SCUBA Level: Beginner – Advanced
Temperature: 27-30°C/81-86°
Visibility: 10-20 m/33-65 ft
Depth: 8-25 m/26-82 ft
SCUBA Level: Medium – Advanced
Temperature: 26-30°C/79-86°F
Visability: 15-30 m/49-100ft
Depth: 18-40+ m/59-130+ ft
What to watch out for
On the island of Koh Bon, there is a special resident. Some boats will say that this is the only place in Thailand where you will see the creature, this is not true, they are just very very rare to see in other parts of Thailand. I’m talking about the Maldivian Sponge Snail, which is a small mollusc that is blue/purple and has 5 lumps on its body which make it look very similar to a sponge. Once you know what you’re looking for, these guys are quite easy to find, but you’re more likely to see them on Koh Bon than anywhere else in Thailand.
