Diving in the Similan Islands: things to know before you go

Thailand, often celebrated as the land of smiles, is also a haven for nature lovers with its 156 national parks, including 9 marine national parks accessible to scuba divers. Among these, the Similan Marine National Park, created in 1982, might be the most famous in the local and international diving community. Located along the Andaman coast, about 70 km off the coast of Khao Lak, the Similan Islands are recognised for their turquoise waters and coral reefs. Many scuba divers, like me, often hear about diving in the Similan Islands first due to the perspective of crossing paths with whale sharks in the famous Richelieu Rock. But did you know this dive site is actually part of another marine national park in Thailand? And this is only one of the key facts you must know when going diving in the Similan Islands.

It had been 10 years since my last visit to Thailand. Before, I had mostly visited Bangkok and Koh Tao (where I did most of my scuba diving training up to Divemaster). This time, I went on a 1-month trip across Thailand, finally exploring the Andaman Coast from Khao Lak to Koh Lanta, including a 4-day diving liveaboard in the Similan Islands. I share everything I have learned here so you can have the best possible experience when planning your diving trip to Thailand. I covered how to get there, where to stay, liveaboard versus day trip, and national park closure, so you have all the information in one place. Ready to explore one of the best dive spots in Thailand?

What is the best season to dive in the Similan Islands?

The Similan Marine National Park is closed from the 16th of May to the 14th of October every year. This annual closure allows the ecosystem to recover from the pressure of tourism at a time when it’s not ideal to visit anyway.

It is important to note that the rainy season in Thailand isn’t all over the country at the same time. There are two rainy seasons. While the part of Thailand from Chiang Mai to Phuket via Bangkok (Northern, Central, and Andaman Coast) has its rainy season from May to October, the Gulf of Thailand (Koh Samui and Koh Tao) has its rainy season from October to January.

Regarding the best diving conditions, water is at its clearest in the Andaman Sea from January to April. Note that the peak season to see whale sharks this year was in February, even if usually January to March is the season to have a chance to see them. In my case, I didn’t see any, just one manta ray in Koh Bon.

You can expect warm water temperatures, usually between 26 and 30°C. I recommend a 3mm full wetsuit (the full wetsuit being in case you run into a jellyfish bloom). However, at the very beginning of the opening season of the Similan Marine National Park, from October to December, water temperatures can be significantly lower. Local divers on my liveaboard reported temperatures down to 21°C in December. Because of the currents, sometimes you can have a much colder thermocline coming from the depths. If you go diving at that time, maybe pack at least a hood, just in case.

The best dive sites in the Similan Islands are not where you expect them to be

The Similan Islands boast numerous dive spots across 11 islands. The archipelago of the Indian Ocean includes nine numbered islands (they have Thai names too, but fun fact, the meaning of Similan in a local dialect is the number 9), plus Koh Bon and Koh Tachai:

• Similan no.1 – Koh Hu Yong
• Similan no.2 – Koh Payang
• Similan no.3 – Koh Payan
• Similan no.4 – Ko Miang
• Similan no.5 – Koh Ha
• Similan no.6 – Koh Payu
• Similan no.7 – Koh Hin Pousar
• Similan no.8 – Koh Similan
• Similan no.9 – Koh Bangu

Similan main archipelago

Each island offers unique topographical features, from shallow coral gardens to steep drop-offs and giant boulders, catering to divers of all levels. From Similan Island No. 1 through Similan No. 9, the dive sites are primarily hard coral gardens, but the topography slowly changes to walls and deeper sandy slopes as you move towards the 9^th island.

My dive log in the Similan Islands:

• Similan no.4 – Honeymoon Bay: 28 m – 46 min – 27°C
• Similan no.7 – West of Eden: 24 m – 52 min – 27°C
• Similan no.8 – Turtle Rock: 24 m – 48 min – 27°C
• Similan no.8 – Donald Duck Bay: 12 m – 45 min – 26°C
• Similan no.9 – Three Trees: 25 m – 47 min – 27°C
• Similan no.9 – Christmas Point: 25 m – 54 min – 27°C

Koh Bon & Koh Tachai

While not technically part of the Similan Islands, the islands of Koh Bon and Koh Tachai are included in the protected area of the Similan Marine National Park. In the end, they offered me my favourite dives of my diving liveaboard due to their impressive topography: an underwater waterfall in Koh Bon and pyramid-shaped rocks covered in large colourful gorgonians in Koh Tachai. If it was fantastic to spot a manta ray in Koh Bon, the schools of batfish, barracuda, and emperor fish in Koh Tachai left the biggest impression on me. Koh Tachai was also my favourite night dive, with lots of nudibranch species to spot in its shallow coral gardens.

My dive log in Koh Bon & Koh Tachai:

• Koh Bon North Beach: 22 m – 50 min – 27°C
• Koh Bon Reef: 18 m – 52 min – 26°C
• Koh Bon South Beach: 22 m – 63 min – 26°C
• Koh Tachai Pinnacle: 26 m – 50 min – 27°C
• Koh Tachai Pinnacle: 26 m – 51 min – 27°C
• Koh Tachai reef: 16 m – 60 min – 26°C

Richelieu Rock & the Surin Islands

And here is the biggest surprise of all: the most famous dive site of the area, Richelieu Rock, isn’t in the Similan Marine National Park but the Surin Marine National Park, at the border with Myanmar. Numerous whale shark sightings are why it became famous in the first place. Although no whale shark decided to say hi to us during my dives, I have to recognise that Richelieu Rock is a one-of-a-kind dive site that almost has it all.

This giant twin pinnacle in the middle of the ocean, with only a tiny piece of rock above the surface, is traversed by nutrient-rich currents, hence the numerous opportunities to encounter pelagic species such as whale sharks. Still, if you don’t have that chance like me, the shoals of emperor fish and jackfish swirling non-stop around Richelieu Rock are quite the sight that would impress any seasoned diver. In addition to mating giant cuttlefish, curious batfish and colourful angelfish, getting a closer look at the rock among the bouquets of bright-coloured soft corals, you might find rare nudibranch species or an entire family of harlequin shrimp munching on sea stars.

My dive log at Richelieu Rock:

• Dive #1: 23 m – 54 min – 27°C
• Dive #2: 21 m – 57 min – 26°C
• Dive #3: 20 m – 69 min – 27°C

What to see underwater in the Similan Islands?

Divers can expect to encounter a wide array of marine life in the Similan Islands. The waters are teeming with schooling fish, green turtles and giant cuttlefish. Night dives add a new dimension to the experience, revealing creatures such as ornate ghost pipefish and various colourful nudibranchs.

Here is the list of popular marine species usually found in the waters of the Similan Islands; I put a tick next to the ones I got to see during my liveaboard:

• manta rays ✔️
• whale sharks
• whitetip reef sharks
• blacktip reef sharks
• leopard sharks
• whale sharks
• spotted eagle rays
• hawksbill sea turtles
• green sea turtles ✔️
• great barracudas ✔️
• giant trevallies ✔️
• giant moray eel ✔️

Now, here is the list of the interesting fish species I personally spotted during my dives from Similan Island no. 4 to Richelieu Rock:

• Batfish
• Moorish idol
• Powder blue tang (surgeonfish)
• Sweetlips
• Lionfish
• Scorpionfish
• Starry pufferfish
• Blue-ring & Emperor angelfish
• Randal’s fusiliers
• Blue-stripped snappers
• Clownfish
• Tomato anemonefish
• Ornate ghost pipefish
• Giant cuttlefish
• Spiny lobster
• Emperor fish
• Blue trevally
• Harlequin shrimp

Regarding nudibranchs, here are the species I spotted with the kind help of the passionate Thai divers present on my Similan liveaboard:

• Girdled glossodoris (Glossodoris Cincta)
• Orange-spotted gymnodoris (Gymnodoris Impudica)
• Gracious roboastra (Roboastra Gracilis)
• Tasselled nudibranch (Kaloplocamus Ramosus)
• Blue-dragon nudibranch (Pteraeolidia Ianthina)
• Ruffled elysia (Elysia Subornata)

Choosing between liveaboards & day trips: my opinion

Once in Khao Lak, visitors have two main options to explore the Similan Islands:

• Day Trips: These are quicker and involve a 90-minute bumpy speedboat ride, each way, from Khao Lak; suitable for those with limited time but still eager to dive in the Similan Islands, you usually do only 2 dives in a day, there are a few options with 3 dives but not all dive centres offer it.
• Liveaboards: Offering an immersive diving experience aboard a large boat, these cruises typically last 3 to 7 days and allow for extensive exploration of the Similan and surrounding islands without the need to return to the mainland every day. If motivated enough, you can do up to 4 dives a day, including a night dive.

When looking into the details, the liveaboard option is more economical for avid divers looking to maximise their time underwater. I chose the liveaboard option because there are too many dive spots within the Similan Marine National Park, and I wanted to see a little of everything, so the liveaboard was much better than doing even 2-day trips as they only have time to go to one specific location each day (and depending on the day of the week, you won’t be able to choose). Then, when you add the marine park feeds and the accommodation cost in Khao Lak, it makes more sense to go for a couple of days (see below).

If you have never done a diving liveaboard before, the Similan Islands might be the best place in the world to get your first experience since the value for money is excellent and the diving conditions are accessible to any diver with at least 20 dives. Note that booking a liveaboard as a solo traveller is absolutely no problem. This is how I did it, and I was paired with another female diver (who became a friend!).

What is the cost of diving in the Similan Islands?

Diving in the Similan Islands is surprisingly affordable when opting for a liveaboard. My 4-day liveaboard in January cost me less than 700€, including accommodation, all meals, unlimited soft drinks and snacks, and up to 15 dives. As someone who did her first liveaboard in the Galapagos, the price difference was quite a shock. Thailand must be one of the most affordable places in the world to experience the fun of a scuba diving liveaboard. Besides, you can choose the length of your cruise to fit your budget. Here are a few examples to give you an idea:

• 4 days/3 nights: from 16,650 THB / 438 €
• 5 days/4 nights: from 20,070 THB / 528 €
• 6 days/5 nights: from 24,860 THB / 654 €
• 8 days/7 nights: from 32,090 THB / 844 €

These are the lowest prices I found for departures in November, but depending on the level of comfort, liveaboards in the Similan Islands can cost up to 2,500 € for an 8D/7N trip. To find the latest prices and last-minute promotion, check liveaboard.com.

Now, it is also essential to take into account the marine park fees to pay extra on top of the price of your dives:

• In the Similan Marine National Park, the entrance fee for liveaboards is 900 BHT (23€), to which you need to add 200 BHT (5€) per day for scuba divers. Scuba diving day trip fees are 700 BHT.
• In the Surin Marine National Park, you pay 500 BHT (13€) for the entrance and a 200 BHT (5€) daily diving fee.

For my 4-day liveaboard in both the Similan and Surin Marine National Parks, I was asked to pay 2000 BHT (about 53€) when I arrived on board in addition to what I had already paid. Make sure to have spare cash on you before boarding. Note that the price of the liveaboards does not include rental equipment.

Regarding diving day trips to the Similan Islands, I checked the price lists of 6 reputable dive centres in Khao Lak, and I found prices go from 4,950 to 5,800 THB (130 – 150€) for a 2-tank day trip. In all cases, don’t forget to add 700 BTH (18 €) of marine park fees to the prices, which also do not include rental equipment.

The price depends mostly on where you want to go and the distance from Khao Lak:

• Richelieu Rock has an average price of 5480 THB / 145 €
• Koh Bon or Koh Tachai, the average price is 5270 THB / 140€
• Similan main archipelago, the average price is 5190 THB / 135€

If this is still too much money, consider taking a snorkelling day trip to the Similan Islands. Prices range from 3100 to 3690 THB (80 – 100 €), averaging 3360 THB (90 €). The marine park fees to add to these prices is 500 THB (13 €). Whatever option you choose, make sure to book early, as there is a maximum number of permits per day.

So if you do the math, taking into account the accommodation (I paid about 40€ per night in Khao Lak for a simple double room) and all the delicious food you get on board instead of going to the restaurant (my average light meal in Khao Lak was 120 THB – 3 €, on the boat we were served food 5 times a day – got to love the pre-breakfast at 6 am), you’ll quickly see how good value the liveaboards in the Similan Islands are.

Rules of scuba diving in the Similan National Marine Park

The Similan National Marine Park enforces specific regulations to preserve its unique marine ecosystems. Adhering to these rules is crucial for maintaining the park’s natural beauty and supporting sustainable diving tourism. Here are the key rules and requirements for diving in the park:

• Daily Visitor Limit: The park allows a maximum of 3,325 visitors daily to minimise environmental impact.
• Entry Requirements: Divers must secure a national park entry ticket at least one day before their visit. You need to have at least a photocopy of your passport on board in case of inspections by National Marine Parks officials.
• Insurance Coverage: All divers must have scuba diving insurance for accident and evacuation.
• Waste management: Single-use plastics are strictly prohibited within the park.
• Drone Restrictions: Drones are prohibited within park boundaries to maintain the tranquillity of the environment and avoid disturbing wildlife.
• Protection of Marine Life: Following the Thai Wild Animal Preservation and Protection Act of 2019, disturbing or harming any marine species is illegal and subject to severe penalties, including a prison sentence of up to four years and fines of up to 40,000 baht (about 1000€).

Compliance with these rules is a legal requirement and a responsibility all visitors share to protect the park’s marine life. It’s important to practice responsible diving by not touching or disturbing marine animals.

Be warned: the park authorities actively monitor compliance through various means, including checking photos and videos. Given the number of divers with cameras in the waters of the Similan Islands, any images showing a diver disturbing or harming marine life can be used as proof. Not only, a diver was recently fined for disturbing a whale shark by pulling its fin, with evidence gathered from social media. Honestly, I’m impressed, big thumbs up to Thailand!

Can you explore the Similan Islands on land?

While the Similan Islands are famed for their vibrant marine life, they also offer beautiful landscapes for on-land exploration. I particularly enjoy Similan Island No. 8, where the iconic Sailrock viewpoint overlooks Donald Duck Bay. This spot offers spectacular panoramic views of the turquoise water bay lined by pure white sand.

Here is another major benefit of doing a diving liveaboard: you can wait for all the day-trippers crowding the island to be gone to enjoy it before sunset. I made sure to be on the first dinghy to land on the beach and headed straight to the trail, climbing to the rock. I got it for myself for 15 minutes (not too bad, right?). The rest of the people who later joined weren’t overwhelming, the atmosphere was friendly, and everyone was helping each other take pictures.

However, it’s important to note that overnight stays on the islands are no longer available. The bungalows and camping sites that once existed on Similan Islands No. 4 and No. 8 have been closed to help protect the island’s fragile ecosystems. This move is part of broader efforts to preserve the natural beauty of the Similan Islands.

Tourism has significantly impacted the islands. In response to overcrowding, the number of daily visitors has been limited to 3,325, down from a previous cap of 3,850 and far below the daily visits that sometimes reached 7,000. Additionally, Ko Tachai has been completely closed off since 2016 to recover from the effects of over-tourism. For the latest information on visiting and protecting the Similan Islands, you can check the official national park page.

Where to stay when exploring the Similan Islands?

Khao Lak serves as the primary base for trips to the Similan Islands; it offers a variety of accommodations ranging from budget guesthouses to luxurious resorts along its kilometres-long sandy beaches. The region has developed significantly, offering more upscale options near the dive sites and ensuring comfort and convenience for divers and travellers alike. Phuket is another option, but I recommend it more after the liveaboard due to the traffic and travel time.

Staying in Khao Lak, before your dive trip

Before setting off for the Similan Islands, you should take the time to explore Khao Lak and its expansive and pristine sandy beaches. The area’s main road stretches over 40 km, but the real charm lies in the quieter side roads and coconut groves that lead to secluded beaches like Khuk Khak Beach, Coconut Beach, and Nang Thong Beach, each offering a unique atmosphere and stunning natural scenery.

Don’t hesitate to rent a scooter to explore them all if you can. I loved Khuk Khak for its wilderness, Coconut Beach for its quiet turquoise waters and cosy beach clubs, and Nang Thong for the sunset by the lighthouse while surfers play in the waves. I had 3 days in Khao Lak and could have used a couple of extra days to visit the old town of Takua Pa or the Khao Na Yak National Park.

I was glad I found the Chu’s Boutique Hotel, as most hotels were fully booked in January, which, weirdly enough to me, is the absolute peak season. The brand-new hotel looked like a small tropical motel with rooms around the pool just big enough to cool off. The private rooms were modern and spotless and included a kettle and a fridge, which, thanks to the 7-Eleven around the corner, was perfect for breakfast and even dinner once.

For those who want to splurge, I also had the opportunity to spend an afternoon at the Avani+ Khao Lak, whose restaurant had the best modern Thai cuisine I had tasted on my entire trip. Their premium offer includes front beach villas and suites with private swimming pools.

On my last day in Khao Lak, before boarding my liveaboard in the evening, I returned to my favourite beach, Khuk Khak, to see its northern part. I ended up drinking a coconut smoothie at the most gorgeous luxury resort in Khao Lak, the Devasom Beach Resort. If you’re looking for true luxury with the most refined Thai style, this is where to go.

Staying in Phuket, after your dive trip

100 km south of Khao Lak Pier, Phuket offers a surprising mix of vibrant nightlife and cultural heritage. Initially put off by Phuket due to the Patong area, I realised how big the island of Phuket actually is and how mistaken I was all this time in avoiding it.

I stayed overnight in a small boutique hotel, Xinlor House, in the middle of the heritage shophouse district, packed with traditional and modern cafés (I loved Rose Espresso Café & Bookhemian). Since I had only a morning to explore before boarding a boat to Koh Lanta, it was perfect to be 10 minutes walking from everything.

This article was written in partnership with the Tourism Authority of Thailand. As always, all my views and opinions are my own and reflect my experience honestly.

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