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Diving Thailand – Dive Sites Thailand – Scuba Diving Similans
Name Koh Bon Similans
Depth 10-50m
Vis 10-40m
Water Temp 24-30c
Level Intermediate+
Our Rating 4.6 Stars
Best Time to Visit October to May
GPS 09-04-114N 97-48-569E West Ridge / 09-03-438N 97-48-769E Pinnacle
  Map of Similan Islands
Manta Ray Koh Bon Thailand

Koh Bon is a small granite island positioned to the northwest of Koh Similans, but still included to be a part of the Similan National Marine Park. The best-known area of the dive site is the west ridge, which drops sharply to the bottom at around 52 metres. Before the dive boat arrives at Koh Bon, divers are briefed about the possibility of seeing Manta Rays. With wingspans of over 5 metres, Mantas are invariably high on any divers wish list of things they want to see. Koh Bon is one of the best places to see and dive with these magnificent creatures. Harmless to humans, they glide past effortlessly feeding on plankton and krill, or hover over cleaning stations motionless in the current. Groups of divers hang around over the west ridge, sometimes holding onto a rock if the current is strong, waiting for the gigantic Manta Rays to cruise past. If you hear tanks being banged frantically, a Manta is in the area. Make sure you keep an eye on your air gauges and computers, as watching Mantas can be a hypnotizing experience and many times divers have run out of air, or gone past their no-deco limits. At this site make especially sure your always stay close to your dive buddy.


It's hard not to be disappointed if you don't see Mantas here, but there is plenty of other stuff to keep most scuba divers happy. Leopard Sharks hang out on the ridge, resting quietly on sandy patches at depths of around 20 metres. Giant Morays poke their huge green heads out from holes in rocks and Nurse Sharks can sometimes be found resting in a small cave - especially early in the morning. If you go deeper, Guitar Sharks can sometimes also be spotted on the sandy bottom at 40 metres+. There is a pinnacle just north of the west ridge. If the current is kind it's possible to jump in at the pinnacle and make your way to the ridge. The pinnacle lies at a depth of approximately 40 metres and rises to a depth of 18 metres. It is carpeted with yellow soft corals and sea fans, and is also visited by Manta Rays. There are occasional visits to Koh Bon from Whalesharks.


Inexperienced divers should remember to watch their depth at Koh Bon and ideally drop somewhere northeast of the ridge where the water is shallower. This area is a cleaning station for Mantas and is a great place to dive if they come. Be wary of the currents here and remember to stop and rest if you start to get breathless. Signal to your dive guide or buddy if you need to. Also at Koh Bon, more than at other sites, thermoclines can be upon you in a matter of seconds. Currents well up from deeper water bringing sediment and particles that can change the 40 metre vis into 1 metre vis, in a matter of seconds. You can usually see them coming, as well as feel the water temperature change several degrees colder when they hit you. Almost as quickly as they appeared, they disappear again, leaving you chilled, but with improving visibility once more.