Similan Islands

Listen, my friend. I will tell you about the Similan Islands and I will not pretend to be neutral. I went in 2022, on a four-day liveaboard out of Khao Lak, between two architecture-research trips that were exhausting me, and I came back unable to talk about anything else for about two months. The Similans are, in my view — and I've snorkelled and dived in a great many places now — the single best stretch of tropical reef I have ever seen.

That is a strong statement. I will defend it.

[IMAGE: https://images.unsplash.com/photo-1582967788606-a171c1080cb0?w=1600&q=80&auto=format&fit=crop | A school of trevally circling above a coral pinnacle in the Similan Islands — visibility about 30 metres, the islands' famous granite boulders dropping into deep blue water]

What the Similans are

A small archipelago of nine granite islands in the Andaman Sea, about sixty kilometres off the western coast of Phang-nga province in southern Thailand. Designated as a national marine park in 1982 and closed entirely to visitors from May to mid-October each year, which is a wise piece of management because it gives the reefs five months of recovery time and is part of why the coral cover here is so remarkable.

The islands themselves are unlike the limestone karst you see at Phi Phi or Krabi — these are granite. Massive rounded boulder formations, some the size of a building, piled on top of each other, creating a coastline that looks geologically impossible until you remember the deep time involved. Above water, the islands are forested and almost entirely undeveloped. Below water, the same boulder geology continues — vast underwater rock formations, swim-throughs, cathedrals of stone covered in soft coral.

This is not a place you can day-trip. Well — you can technically take a fast-boat day-trip from Khao Lak which gets you a snorkel at one site and an hour on a beach. Don't. The only sensible way to see the Similans is on a liveaboard, three or four nights at minimum.

The liveaboard model

A liveaboard is a small dive boat — typically 16-24 passengers — that sails to a remote dive area and stays there for several days, with you living on board. Three meals a day cooked in the galley. Twin cabins or, if you pay more, doubles. Three or four dives a day, with surface intervals for eating, reading, dozing on the upper deck.

The Similan liveaboards leave from Tap Lamu pier, about an hour south of Khao Lak. A typical four-day, four-night trip includes thirteen to fifteen dives, all meals, and pickup from your hotel. Costs about 1,200-1,800 USD depending on the boat and the cabin grade. Yes, this is more than land-based diving. Yes, it is worth the difference. The boats anchor at the islands themselves, which means you wake up in the middle of the marine park, do your first dive at first light when the water is at its clearest, and have those dive sites essentially to yourselves before any of the day-trippers arrive.

The dive sites that justify the trip

Of the dozens of named sites in the park, a handful are world-class:

Elephant Head Rock. A submerged pinnacle between islands seven and eight, with vast granite boulders forming swim-throughs and overhangs at depths from twelve to thirty metres. The current can rip here on a strong day; you ride it. The soft corals on the swim-through walls are brilliant orange and purple. We saw a six-foot Napoleon wrasse here on our second dive that came right up to the camera.

Christmas Point. Off island number nine, north end of the archipelago. Massive boulder field, swim-throughs, the full menagerie — manta rays in season (February-April), reef sharks, sometimes a leopard shark sleeping on a sand patch. One of the better sites in Asia.

Boulder City. Self-explanatory — an underwater field of granite boulders the size of cars, 16-30m, covered in coral. Schools of fusiliers and snappers swirl in the gaps.

East of Eden. The sad story. Was once one of the most beautiful coral gardens in the marine park, badly damaged by the 2010 bleaching event. Has been recovering. A monitoring site as much as a dive site, but the recovery is real and visible compared to ten years ago.

Richelieu Rock. Technically in the neighbouring Surin marine park, about 30 km north of the Similans, but most longer Similan liveaboards include it. A small isolated pinnacle in open water, regarded by many as the best single dive in Thailand. Whale shark season is February-May; even outside that window the marine life density is extraordinary.

When to go

The marine park is open mid-October to mid-May. Within that window:

November-December — opening of the season, the seas are calm, vis is excellent, but the water can be slightly cooler (26-27°C) and the manta rays haven't really started showing up yet.

January-February — peak season. Expensive, busy, but the diving is at its best.

March-April — manta and whale shark peak. Crowds remain heavy. The end of the dry season.

Mid-October and mid-May — shoulder. Worth knowing the marine park can be closed early or late if the monsoon comes early or late. Worth booking with operators who will refund or rebook in that case.

I went in late February. Conditions were textbook.

Picking a liveaboard operator

Some things I look for, having dived enough liveaboards to have opinions:

• Boat age and maintenance. A well-maintained twenty-year-old wooden boat is fine; a poorly-maintained five-year-old steel hull is not. Ask about the last refit.
• Crew-to-passenger ratio. Good operators run two divemasters for sixteen divers, plus a separate boat crew, plus the chef.
• Briefings. A serious operator briefs every dive in detail with a whiteboard map. Cattle-boat operators give you a five-minute hand-wave.
• Dive group sizes. Maximum four divers per divemaster underwater. Six is too many.
• NITROX availability. Nitrox extends bottom time for repetitive dives, which is exactly the situation on a liveaboard. The good operators include it free.

I dove with Wicked Diving on the recommendation of an old friend. Smaller boat (16 passengers), strong environmental ethic, all fees included. There are several others in the same bracket — South Siam Divers, Khao Lak Scuba Adventures. Avoid the cheapest options.

What to bring

Bring: your dive cert card (everyone forgets), a 3mm wetsuit (the water is warm but on five dives a day you will feel it), a torch for the night dive on day three, sea-sick tablets for day one if you are prone (the open-water crossing to the islands is about three hours and can be choppy), a dry bag for camera gear, a refillable water bottle (single-use plastic is being phased out at most operators).

Don't bring: heavy luggage. Cabins are small. Soft duffel only. Leave your big roller bag at your Khao Lak hotel.

Combining the trip

Khao Lak itself, the liveaboard launching point, is a quiet beach town and a much nicer place to spend a few pre-and-post nights than Phuket. Three days at Khao Lak before or after the liveaboard is a good plan. The wider Thailand country guide covers the southern coast and connecting routes to the Andaman islands, the Gulf, and overland to Myanmar. For tours in Thailand including non-liveaboard options, the listing has a few good multi-day combinations.

For another reef-diving comparison, Koh Tao on the Gulf side is a different kind of trip — cheaper, more accessible, less spectacular but excellent for new divers.

Official sources

The Department of National Parks Thailand page for Mu Ko Similan has the marine park rules, current visitor caps, and the seasonal closure dates. The PADI dive shop locator lets you verify the certification status of any operator.

A small note on the marine park rules

The Department of National Parks has tightened the rules considerably since the 2018 closure. Each visitor must now arrive on a registered boat (no private craft inside the park boundary). Daily visitor caps were introduced — about 3,850 visitors a day across the park, with about 525 of those on liveaboards. Touching coral is a 5,000-baht fine and the rangers do enforce it. Single-use plastic is banned on island visits.

These rules have made the experience considerably better for everyone. The day-trip beaches at Donald Duck Bay (Island 8) and Honeymoon Bay (Island 4) are managed with shaded pavilions and timed entry. Liveaboards are restricted to specific anchorages, which means even on a busy week you can have a dive site mostly to your boat alone. The contrast with the chaotic pre-2018 management is night and day.

Final word

I have written about a great many extraordinary places over the years on BugBitten — going back to my early Brasilia entries — and the Similan Islands sit very near the top of my list. Not because the diving is the most extreme, or the most exotic. Because the combination of geological drama, coral health, marine life density, and the sheer remoteness of the place produces an experience that makes you understand, viscerally, what these reefs were like before everything started going wrong fifty years ago. The Similans are what reefs used to look like.

Four nights minimum on a liveaboard. Pick a small operator. Go in February if you can. Bring the camera but know that the photographs will not do it. My friend, this is one of those trips. Look at that.