Similan Islands Liveaboard Trip Report December 2023

Uncharacteristically cold waters during December 2023 in the Similan Islands brought a whole bunch of new marine life up from the deep. Here’s some photos from a very chilly liveaboard trip

Marble Ray on the move over boulder © chris@divehappy.com

Cold, cold, so cold. Diving in the Similan Islands typically involves balmy temperatures of 28 to 29 degrees celsius in the water. Many divers just go with boardshorts and a thin neoprene top it’s so warm. That was definitely not a wise idea during December 2023, when temperatures in the water dropped to a chilly 23 degrees.

Jacks over the top of Richelieu Rock © chris@divehappy.com

It obviously wasn’t 23 degrees as soon as you hit the water – the real cold temperatures were reserved for going down below 15 metres. That’s where you can encounter the joy of the Green Monster, the local name for the cold current which sometimes rolls in from the deep, making the water feel like you’re looking at a shimmering mirage but with a drop in temperature that definitely lets you know you’re not in the desert.

Richelieu soft corals and glassfish © chris@divehappy.com

The upside of the the downturn in temperature is that it means a lot of sharks and rays come up shallower than normal, straying into the 30 metre and above zone divers typically wander around in.

Barracuda from below, Richelieu Rock © chris@divehappy.com

As such we had sightings of rays on several dives, including an absolute whopper of a blotched fantail ray, easily a metre across its main body, resting between the big rocks at Christmas Point, along with a smaller, more active marble ray further into the deep.

Christmas Point big marble ray resting © chris@divehappy.com

The cold water certainly hadn’t scared off the usual suspects to be found on a Similans liveaboard – Richelieu Rock in particular was absolutely epic for fish action, with electric activity all over the pinnacle.

Richelieu Rock anemones with cyclone of glassfish © chris@divehappy.com

Glassfish in their thousands shimmered around the soft corals, arcing like a silver ribbon just for a moment and then shape shifting as one.

Fusiliers running over the anemones, Richelieu Rock © chris@divehappy.com

Hundreds-strong schools of fusiliers would sweep across the famous soft corals at the top of the rock, momentarily blocking out the sun because there was so many.

Jacks, Richelieu Rock © chris@divehappy.com

Recommended Similan Liveaboards October 2025 to May 2026

Blue Dolphin Liveaboard

A mid-range liveaboard with 7 cabins for 16 people. Check availability and pricing

The Phinisi Liveaboard

A Similan mid-range liveaboard with 7 cabins for 18 people.Check availability and pricing

Smiling Seahorse Liveaboard

A mid-range liveaboard with 8 cabins for 16 people. Check availability and pricing

The Junk Liveaboard

A mid-range liveaboard with 6 cabins for 18 people. Check availability and pricing

Fusiliers running © chris@divehappy.com

By way of complete contrast to Richelieu, Ao Pakkad in the Surin Islands provided for a beautiful and serene early morning dive before heading to the mayhem of the Rock.

Ao Pakkad staghorn and fish © chris@divehappy.com

Ao Pakkad is a huge hard coral garden that has been left largely untouched. The corals here are super old, super dense and largely pristine – it is a joy to see a reef so untouched. It’s super shallow, from a metre down to 10 metres, and so the sunlight streams down onto the corals too.

Glassfish cyclone over table coral, Ao Pakkad © chris@divehappy.com

The garden is characterised by corals growing on top of corals, all shapes and sizes encroaching and entwining on each other.

Ray and two divers © chris@divehappy.com

The cold water had brought rays up even into the shallows of Ao Pakkad, with several of them sat on the sand where the reef runs out.

Ao Pakkad reef layers © chris@divehappy.com

The coral layers of Ao Pakkad’s reef can be super colourful

Staghorn with glassfish © chris@divehappy.com

There are healthy outcrops of staghorn corals which glassfish love to gather around, along with big table corals that also provide shelter.

Glassfish over table coral, Ao Pakkad © chris@divehappy.com

If you're interested in doing a Similan liveboard yourself, see Diving The Similan Islands: A Quick Guide for a breakdown of how a liveaboard trip works and why the Similans are so special for diving.

Emperorfish over the reef at Richelieu Rock © chris@divehappy.com

Despite it being quite murky at Richelieu Rock, it was spectacular in terms of the sheer amount of fish gathered there.

Jacks running, Richelieu Rock © chris@divehappy.com

Epic runs of emperorfish across the rock and jacks running from out of the depths

Glassfish cyclone in front of Richelieu Rock pinnacle © chris@divehappy.com

While there are always a lot of glassfish at Richelieu, on one dive there were so many you couldn’t see the base of the rock – thousands upon thousands of them like a cyclone sweeping through.

Fish stampede at Richelieu Rock © chris@divehappy.com

The jacks and rainbow runners like to hunt together in hundred strong packs – being in the middle of this as the fish shoot past you inches away from your face is not an experience you’re likely to forget.

Two rays, Richelieu Rock © chris@divehappy.com

The cold water was bringing up more rays from the depths to Richelieu’s flat sand around the pinnacle. At one point we saw a group of five of them all resting on the sand.

Glassfish and soft coral Richelieu Rock © chris@divehappy.com

And despite the murky conditions, there was still sunlight and Richelieu’s signature soft red corals bursting with colour near the top of the rock.

Fish run from the depths, Richelieu Rock © chris@divehappy.com

The runs from the jacks and rainbow runners was not a one-off, blink and you’ll miss it kind of event.

Fish stampede, Richelieu Rock © chris@divehappy.com

They do this regularly – if you stay in one place on the dive site you’ll probably see them run four or five times.

Lionfish get a raw deal because they’ve accidentally invaded the Caribbean, but they’re great subjects for photography.

These two emperorfish were too interested in finding food to be bothered by the camera.

The cold water had also brought a big school of sweetlips up to around 30 metres at the end of Koh Bon ridge – more used to seeing these guys in such big numbers in Indonesia.

When the current’s too strong and you get pushed off Koh Bon’s ridge into Koh Bon Bay, there’s still some surprises around, like these two cuttlefish and a puffafish getting cleaned.