Similan Islands Snorkeling Guide: Everything You Need to Know Before You Go

The Similan Islands are a group of nine granite islands in the Andaman Sea, about 70 km off the coast of Phang Nga Province. They form a marine national park that is widely considered to have some of the best snorkelling and diving in the world. As someone who has snorkeled and dived here dozens of times, here is a complete guide to help you plan the perfect trip.

When to Go: The Park Schedule

The Similan Islands National Park is open only from mid-October to mid-May each year. From May to October, the park is closed entirely to allow the marine ecosystem to recover during the monsoon season. This is strictly enforced — no boats are permitted. Plan accordingly: if you are visiting Thailand between June and September, you will need to choose an alternative (Koh Tao in the Gulf of Thailand is the best substitute for snorkelling during these months).

• Best months: November to March. Clear water, calm seas, pleasant temperatures.
• Avoid: Late April to mid-May. The water visibility drops and the seas can be rough before the park closes.
• Peak crowds: December 20 to January 10 and Chinese New Year. Book well in advance.

Tour Types and Costs

Speedboat Day Trip

The most popular option. Departures from Khao Lak (closest, 1-hour boat ride) and Phuket (2-hour boat ride). Tours typically include two or three snorkelling stops, a visit to Donald Duck Bay or another beach, lunch on the boat or on an island, and snorkel gear. Cost: 3,000-4,500 THB ($86-$129 USD) per person, depending on the operator and departure point.

Liveaboard (2-4 days)

For the best experience, book a liveaboard boat. You sleep on the boat for 2-4 nights, snorkel or dive at multiple sites (including less-visited sites that day-trippers do not reach), and enjoy the islands at sunrise and sunset when the day-trip crowds are gone. Cost: 8,000-20,000 THB ($229-$572 USD) depending on the boat, duration, and whether you are snorkelling or diving. This is the option I recommend for anyone serious about seeing the best of the Similans.

Private Charter

If you are travelling with a group, a private speedboat charter costs about 18,000-25,000 THB ($515-$715 USD) for a full day for up to 8-10 people. You can customise your itinerary, avoid crowded sites, and go at your own pace. This can work out cheaper per person than a group tour if you have enough people.

Top Snorkelling Sites

Christmas Point (Koh Ba Ngu, Island 9)

The northernmost site, known for dramatic underwater rock formations and large schools of fish. You may see barracuda, trevally, and occasionally reef sharks. The visibility here is often the best in the park (30+ metres). Best for confident snorkelers — there can be currents.

East of Eden (Koh Pa-Young, Island 7)

A sloping coral reef with enormous variety. This is where you are most likely to see sea turtles, which feed on the seagrass beds. The coral here is in excellent condition, with both soft and hard corals. Suitable for all levels.

Anita’s Reef (Koh Ha, Island 5)

A gentle sloping reef perfect for beginners. The coral starts at about 2 metres and drops to 25 metres, so snorkelers can see plenty while divers go deeper. Look for garden eels in the sand, clownfish in the anemones, and giant clams embedded in the coral.

Donald Duck Bay (Koh Miang, Island 4)

Named for a rock formation that resembles Donald Duck’s profile, this is the primary beach stop for day trips. The beach itself is stunning — giant boulders, white sand, crystal water. The snorkelling off the rocks at the north end of the bay is decent, though not the best in the park. This is also where the park headquarters and ranger station are located.

What You Will See

• Fish: Clownfish (anemonefish), parrotfish, angelfish, butterflyfish, wrasse, triggerfish, lionfish, and large schools of snappers and fusiliers.
• Larger species: Sea turtles (green and hawksbill), reef sharks (blacktip and whitetip), barracuda, trevally, and occasionally manta rays (February to April) and whale sharks (rare, but possible in March-April).
• Coral: Both hard corals (brain, staghorn, table) and soft corals. The Similans have some of the healthiest remaining coral in Thailand, though bleaching events have affected some areas.
• Topside: The distinctive giant granite boulder formations that give the islands their character, white-sand beaches, and monitor lizards on the beaches.

National Park Fees

• Entrance fee: 500 THB ($14 USD) for foreign adults, 300 THB ($8.50 USD) for foreign children. Thai nationals pay less.
• This fee is usually included in the price of your tour. If it is not included, you will pay it at the park. Check when booking.
• The park is cashless at the headquarters — bring exact cash or be prepared for a digital payment via the Thai national park QR code system.

What to Bring

• Reef-safe sunscreen: Chemical sunscreens (containing oxybenzone or octinoxate) damage coral. Use a mineral (zinc oxide or titanium dioxide) sunscreen instead. Many tour operators now sell reef-safe sunscreen on the boat.
• Rash guard or swim shirt: Protects from sunburn without sunscreen, and also protects from jellyfish stings.
• Seasickness medication: The speedboat ride can be bumpy, especially on the return trip in the afternoon. Take medication 30 minutes before departure.
• Underwater camera or GoPro: You will want to remember this. A floating wrist strap is essential.
• Towel and dry clothes: For the boat ride back.
• Waterproof bag: For phone, wallet, and camera.

Responsible Snorkelling

1. Do not touch coral. Even a light touch can kill coral polyps, which take decades to recover.
2. Do not touch or chase marine life. This includes turtles, sharks, and fish. Maintain a respectful distance.
3. Do not feed fish. It disrupts their natural feeding behaviour and can cause reef damage.
4. Do not stand on coral. If you need to rest, float on your back or find a sandy patch. Never stand on coral.
5. Choose operators with responsible practices. Avoid operators that crowd snorkellers together or allow touching of marine life. Ask about their environmental policy when booking.

How to Book

Book through a reputable dive shop or tour operator rather than a street stall. Good operators include Wicked Diving, Sea Dragon Dive Center, and Similan Dive Center (all based in Khao Lak). If you are in Phuket, most dive shops offer Similan trips, though the longer transit means less time in the water. Book at least a few days in advance during peak season — the best boats fill up quickly.

The Similan Islands offer an underwater world that is increasingly rare in Southeast Asia. Snorkel gently, choose responsible operators, and you will understand why these islands are considered one of the planet’s great marine treasures.