May 15, 2026, was the last day of access to Mu Ko Similan National Park before the annual monsoon closure. Its reopening is expected in mid-October. If you are preparing your first diving cruise in Thailand, this date matters before the boat, before the site, and before the price.
Our old page sold trips “from Phuket” lasting one to eight days, between 3,600 and 32,900 baht, manta rays observed “regularly,” and five whale sharks seen in a single dive. None of this was dated or sourced. It also listed Richelieu Rock among the Similan islands, which is incorrect.
We have redone everything using the framework of our other destinations: level, current, season, supervision, and fallback plan.
When is Similan National Park open?
The park generally opens from October 15 to May 15. In 2025, the Thai Department of National Parks (DNP) closed it from May 16 to October 14, according to the announcement published by the Thai government, and the Thai press later confirmed a season open until May 15, 2026. Outside this window, no tourist trips enter.
For the 2026-2027 season, no official dated announcement was found at the time of our update.
The usual schedule suggests a reopening on October 15. Planning does not mean confirming. However, some operators already sell cruises for the very week of reopening, without always stating what they do if the park opens later or if the sea remains rough in the first days. Ask for this in writing. Refund, postponement, or itinerary outside the park, the answer changes what you buy.
Since October 15, 2025, each visitor must also purchase an electronic ticket online, in advance or on the same day before 8 a.m., according to the Thai government. Your operator often handles this. Verify it.
Leaving from Khao Lak or Phuket: what changes?
Most boats for the Similan depart from Thap Lamu port, near Khao Lak, in Phang Nga province. The archipelago is located 65 or 70 kilometers from the coast, according to public data consulted. From Phuket, you must add a road transfer or a longer crossing.
“From Phuket” does not specify where the boat departs.
Many offers sold “from Phuket” actually include a morning minibus to Thap Lamu, then a speedboat crossing to the archipelago, with a return by the same route at the end of the day. Count this time. A day starting before dawn tires you before the first dive. And fatigue reduces your margin if conditions get complicated underwater. Multi-day cruises depart from Khao Lak or Phuket depending on the operators, and some extend to the Surin Islands and Richelieu Rock.
If you stay in Phuket for the rest of your trip, the south coast offers other day options, which we detail in our guide to diving sites in Krabi and Phi Phi. The choice of departure point then determines your wake-up time more than the site.
Similan, Koh Bon, Koh Tachai, Richelieu Rock: what is in the park?
Mu Ko Similan Park includes eleven islands. To the original nine islands were added Koh Bon and Koh Tachai in 1998. Richelieu Rock belongs to another park, Mu Ko Surin, and the Boonsung wreck is a coastal dive located outside both parks, off Phang Nga province.
| Site | Park | Indicative Level | To check before leaving |
|---|---|---|---|
| Islands 1 to 9 (Similan) | Mu Ko Similan | Variable depending on the site, from snorkeling to wall diving | Planned site, maximum depth |
| Koh Bon | Mu Ko Similan | Depending on the current of the day | Current, ascent in open water |
| Koh Tachai | Mu Ko Similan (island closed to visitors since 2016) | Depending on the profile chosen by the guide | Sites authorized this season |
| Richelieu Rock | Mu Ko Surin | Isolated pinnacle, base around 30 to 37 m (indicative) | Exposure, safety stop buoy |
| Boonsung Wreck | Outside park | Depending on the profile chosen by the guide | Depth, sea conditions |
Koh Tachai requests clarification. In May 2016, the DNP closed the island to visitors due to overcrowding and degradation, according to Divernet at the time. Diving remained allowed at certain sites around the island, without landing, and the park’s public fact sheets updated in 2026 still describe this situation. Ask which Tachai sites your boat is allowed to dive this season.
Our old page promised visibility at Richelieu Rock “greater than 20 meters,” mantas, and whale sharks as if from a catalog.
But none of these figures were dated. In an article published in 2025, DAN describes Richelieu Rock as completely exposed to the elements from October to March, with no island or shelter for miles around, and visibility peaking from February to May. Whale sharks are sometimes seen there. Nothing is guaranteed. Clear water says nothing about the current.
Cruise or day trip: for what level?
The level depends on the site, the current of the day, and the profile chosen by the guide, not on the entire archipelago. A center can offer certain sheltered sites of the Similan to an Open Water diver. Exposed pinnacles like Koh Bon or Richelieu Rock require real ease in open water, regardless of the certification displayed.
The current decides more than the photo.
The park also limits the number of visitors. The Thai press reported in 2021, then again in 2024, a daily cap of 3,850 people, including 525 spots reserved for diving. If your dates are fixed, ask the operator if they already have tickets for your outing day. The entrance fee displayed for a foreign adult is 500 baht, and 250 baht for a child aged 3 to 14, according to public fact sheets updated in June 2026. Ask if it is included in the price.
However, the real choice concerns the format. Since October 2018, no accommodation exists on the islands, so you either sleep on land or aboard a cruise boat. The day trip brings you back to Khao Lak each evening and costs in repeated transfers. The cruise chains more dives and reaches distant sites, but it commits you for several days without an easy exit if you don’t feel well.
On the boat as in the water, keep your fins away from the bottom. The reasons why you should never touch marine life apply even more in a park that closes five months a year to let its reefs recover.
What fallback plan and safety should you plan?
Your fallback plan depends on the cause of cancellation. If the swell closes a site, the guide can choose a more sheltered bay in the park. If the entire park is closed, the Similan and Surin are closed at the same time, and there remain coastal sites outside the park like the Boonsung wreck, when the sea allows.
The monsoon also affects the coast.
Thus, a stay scheduled for late May or early October leaves you little choice. On an exposed pinnacle, the ascent is often done in open water, under a decompression buoy that you know how to deploy. If you have never done it, say so at the briefing. The guide will adapt the dive. Further north, cruises to the Mergui Islands in Myanmar depart from Ranong, with their own formalities and season.
On the emergency side, Bangkok Hospital Siriroj in Phuket presents on its site a multiplace hyperbaric chamber open 24 hours a day for decompression accidents, information noted in October 2026 that is best cross-checked with your dive insurance before departure. Also ask the boat how it evacuates a diver from the archipelago. The answer takes a minute.
In short, this fallback plan has a concrete cost: a day of margin in your stay, a return flight that does not coincide with your last dive, and insurance that covers the chamber. Would you book it this way?
FAQ
When are the Similan Islands open?
The park generally opens from October 15 to May 15. In 2025, the DNP closed it from May 16 to October 14. Check the reopening date of the current season before paying a deposit.
Should you depart from Phuket or Khao Lak?
Most boats depart from Thap Lamu, near Khao Lak. An “from Phuket” offer often adds a road transfer. Ask for the departure port and pickup time.
Is Richelieu Rock part of the Similan Islands?
No. Richelieu Rock belongs to the Mu Ko Surin National Park. Many cruises combine the two parks, which close on the same dates.
Can you dive at Koh Tachai?
The island has been closed to visitors since 2016. Some dive sites around the island remained accessible, without landing. Ask your operator which ones are allowed this season.
How much is the park entrance fee?
The public fact sheets updated in June 2026 indicate 500 baht for a foreign adult and 250 baht for a child aged 3 to 14. The rate may change. Ask if it is included in the price of your trip.
Sources
- Similan Islands and Surin Islands to be temporarily closed from 16 May to 14 Oct 2025 (National News Bureau of Thailand, Thai government, 2025)
- Thailand’s Surin Islands (DAN, Alert Diver, Mike Bartick, 2025)
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