It’s no big secret where the absolute best diving in Thailand is, it’s just that most prefer the easy diving in the sheltered Gulf of Thailand or impromptu day trips out of Krabi, Phuket and Ko Phi Phi.

A trip out to Mu Ko Similan National Park in the Andaman Sea is a slightly more serious adventure. One that requires at least a little forethought, not least because the park is closed during May to October when the south-west monsoon sweeps across the Indian Ocean.

The Similan Islands National Park is home to a collection of granite islands, boulders and pinnacles and its location 55 km offshore means that it’s largely unaffected by water quality issues, marine plastic pollution and being a marine park – commercial fishing.


Boasting terrains facing the open Indian Ocean and the more sheltered coastal water, it provides a wide variety of habitats and hence a great diversity of marine life. You’ll find all the usual reef suspects from surgeon fish to rabbitfish, Moorish idols to butterflies, all manner of wrasse and trigger fish, goatfish and snapper, and in numbers you won’t see in many other places. Add to this mix, all the unusual reef suspects, such as blennies, scorpionfish, Pixie Goatfish and pipefish including that Holy Grail of pipefish – the Ghost Pipefish – and you start to understand why it’s acknowledged as the best diving in Thailand.

‘Mu Koh’ actually means ‘group of islands’ and the nine islands of the Similans go by numbers as well as their names hence Similan #7 is Koh Payu.

Well managed as a marine park (there is a per dive/per day fee), Similan #1, #2 & #3 are currently closed for re-habitation, but there are still over 20 dive sites amongst the other islands, and the three pinnacles that have been annexed into the Similan National Park: Hin Pusa or ‘Elephant Head Rock’, Koh Bon and Koh Tachai.

Though all composed of solid granite, the islands and pinnacles have unique characteristics and terrain, from ridges to bays, monolithic walls and slots, and many swim throughs – a veritable adventure playground for divers.

Collectively they offer so much different terrain, I overheard a diver comment that “this place would be great fun even without the fish!”. One coral stack in Koh Bon, encrusted on top with hard corals and adorned underneath with soft corals, is home to a pair of the biggest giant morays we’ve ever seen in our lives – bodies thicker than your thigh. They dwarfed the tiny ringed pipefish hiding in the same overhang, while sea snakes zigzag along the sand nearby.

At Koh Tachai we watch a group of white collared butterflyfish hang in the lea of a giant gorgonian fan whilst cleaner wrasse work to their way methodically around the group. The nearby walls are littered with nudis and at any given moment you might see a turtle casually cruise right through your dive group.

Koh Bangu has possibly the most dramatic terrain with slab-like boulders 15m high, hiding deep slots between them, and dim, narrow swim throughs below where you’re guaranteed to surprise a whole bunch of big-eyed soldier and squirrelfish sitting out the day – waiting for darkness and their turn to hunt.

To dive the Similans, you should allow yourself at least a week. There are liveaboard dive boats departing from Phuket and Khao Lak with differing itineraries, some of which include the fabled Richelieu Rock – a-whole-nother dive adventure in itself!