Scuba Diving in Similan Islands

Diving in Similan Islands

Diving in Similan Islands is what put Thailand on the international dive map. The core chain is nine granite islands sitting in the Andaman Sea about 80 to 100 km northwest of Phuket. Mu Ko Similan National Park expanded in 1998 to include Koh Bon and Koh Tachai, so the park itself now covers 11 islands. The underwater scenery is unlike anywhere else in the country. West sides of the islands are dramatic boulder gardens with swim-throughs and arches. East sides are gentler sloping reefs covered in hard and soft corals. Visibility regularly hits 30 m (98 ft) and pushes past 40 m (131 ft) on the best days.

The park closes May 16 through October 14 every year to let the reefs recover from monsoon and tourist traffic. That means a hard window: late October through mid-May is your only shot. Water temps run 27 – 31 °C (81 – 88 °F), warmest in April, so a 3 mm shorty is plenty for most divers and many go skin-only.

You can dive the Similans on a day trip from Khao Lak (60 to 90 minutes by speedboat to the islands) or, more commonly, on a 3- to 5-night liveaboard that strings together the best sites along with Koh Bon, Koh Tachai, and Richelieu Rock further north. Liveaboards typically cover 11 to 14 dives. Day trips give you 2. The advantage of going long: peak sites like Boulder City and Elephant Head Rock are easier to dive at slack tide, and a liveaboard lets you time them right.

Marine life ranges from reef regulars (parrotfish, snapper, barracuda) to the headliners divers fly in for: manta rays, whale sharks, leopard sharks, and the occasional eagle ray school. Whale sharks peak February through April, with January also a strong month. Most Similan dives sit in the 5 – 30 m (16 – 98 ft) range, with a few sites pushing 35 – 40 m (115 – 131 ft) for advanced divers.

Best dive sites in Similan Islands

The best dive sites in Similan Islands are mostly on the west side, where granite boulders pile up underwater to form a maze of swim-throughs, tunnels, and pinnacles. Currents vary site to site and tide to tide. Below are five of the most-booked sites, ranked by broad appeal.

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Elephant Head Rock

Elephant Head is the showpiece of the Similans. A jumble of car-sized granite boulders piled in shallow water and sloping down past 40 m (131 ft), with channels, swim-throughs, and tunnels in every direction. You'll thread between rocks the size of buses with light pouring in through gaps overhead, then drop out onto sand where leopard sharks sometimes rest. Currents can pick up here, so this one's best at slack tide. Save it for later in your liveaboard when buoyancy is dialled in.

• Depth: 5–40 m (16–131 ft)
• Visibility: 25–40 m (82–131 ft)
• Current: Moderate to strong
• Level: Advanced
• Key species: Leopard shark, schooling barracuda, octopus, scorpionfish, lionfish

Christmas Point

On the far north of the Similan chain off Koh Bangu (Island 9), Christmas Point is another granite boulder site with a famous swim-through at around 24 m (79 ft) that pops out onto a coral garden. The west side drops to 35 – 40 m (115 – 131 ft) and is covered in soft corals and sea fans. Schooling fish work the blue and reef sharks pass through. Whale sharks show up here in season. Depths and the swim-through profile make it an Advanced site.

• Depth: 8–35 m (26–115 ft)
• Visibility: 25–40 m (82–131 ft)
• Current: Moderate to strong
• Level: Advanced
• Key species: Whale shark (Feb–Apr), reef shark, schooling jacks, fusiliers, moray eel

Anita's Reef

Anita's Reef is the standout easy dive on the Similan route, stretching from the gap between Islands 5 and 6 down to the southern tip of Island 5. A gentle sandy slope holds coral bommies, table corals, and staghorn formations, with anemones on the bommie tops hosting clownfish and porcelain crabs. Currents are mellow and the profile is forgiving, which makes it the standard check-out dive on most liveaboards. Good first dive of the trip, suitable for all levels.

• Depth: 5–28 m (16–92 ft)
• Visibility: 20–30 m (66–98 ft)
• Current: Gentle
• Level: All levels
• Key species: Anemonefish, porcelain crab, blue-spotted ray, butterflyfish, hawksbill turtle

Boulder City

Far south end of the Similan chain, off Island 3. Boulder City is a deep granite site with strong viz and currents that range from manageable to ripping. The dive starts at 12 m (39 ft) on a plateau covered in hard corals and bommies, then drops past 40 m (131 ft) along the boulder slope. You're in deep blue water here, so eyes off the reef and into the blue: barracuda schools, dogtooth tuna, and sometimes whitetip reef sharks cruise the edges.

• Depth: 12–40 m (39–131 ft)
• Visibility: 20–35 m (66–115 ft)
• Current: Moderate to strong
• Level: Advanced
• Key species: Barracuda, dogtooth tuna, whitetip reef shark, blue-spotted ray, scorpionfish

North Point

The northernmost dive site in the main Similan chain, off Koh Bangu (Island 9). Granite boulder formation sloping into deep water, with a separate pinnacle to the northwest covered in giant sea fans. Currents run medium to strong and visibility holds up well in the blue. A great spot for divers comfortable with deeper profiles and a bit of flow.

• Depth: 12–40 m (39–131 ft)
• Visibility: 25–40 m (82–131 ft)
• Current: Moderate to strong
• Level: Advanced
• Key species: Giant sea fans, reef shark, schooling snapper, hawksbill turtle, sea fan goby

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Best time to dive Similan Islands

The best time to dive Similan Islands is between late January and mid-April, when seas are calm and visibility regularly tops 30 m (98 ft). The park is only open from October 15 to May 15 each year, so the diving window is fixed. Outside those dates the boats stop running, the reefs are closed to visitors, and monsoon swell makes the crossing rough anyway.

February and March are the safest bet for serious divers. If you're chasing whale sharks and mantas, aim late February through early April when sightings peak around Koh Bon, Koh Tachai, and the northern sites. January is also a strong whale shark month.

Diving conditions

Diving conditions in Similan Islands are about as good as Thailand gets. Water is warm, visibility is consistently in the 20 – 40 m (66 – 131 ft) range, and most sites are sheltered enough for relaxed dives. The main thing to plan around is current at the boulder sites on the west.

Marine life in Similan Islands

Marine life in Similan Islands swings between two scenes depending on which side of the islands you're on. East-side reefs are macro and coral-garden territory: turtles, octopus, nudibranchs, anemonefish, and small reef stuff. West-side boulder dives are where pelagic action happens, with reef sharks, schooling barracuda, and bigger visitors passing through. The northern sites (Koh Bon and Koh Tachai, also inside Mu Ko Similan National Park since the 1998 expansion) are the manta and whale shark hotspots.

• Pelagics: Whale shark, manta ray, leopard shark, whitetip and blacktip reef shark, dogtooth tuna, giant trevally, barracuda, eagle ray
• Macro life: Nudibranchs, octopus, ghost pipefish, mantis shrimp, frogfish (occasional), seahorses
• Reef dwellers: Hawksbill turtle, parrotfish, snapper, fusilier, anemonefish, moray eel, scorpionfish, lionfish, blue-spotted ray, sea fan goby

The Similans sit inside Mu Ko Similan National Park, established in 1982 and expanded in 1998 to include Koh Bon and Koh Tachai. The annual May-to-October closure exists specifically so reefs can recover from monsoon damage and tourist pressure, and park rangers enforce mooring buoy use and no-touch rules. Koh Tachai island itself has been closed to landings since 2016 for conservation, though the dive sites around it remain open.

Whale sharks: late January to April, especially around Koh Bon, Koh Tachai, and Elephant Head Rock

Whale shark sightings peak in late January through April when plankton-rich currents push through the park's northern sites. Koh Bon and Koh Tachai are the most reliable encounters; Elephant Head Rock and Christmas Point also score regularly during this window.

Manta rays: February to April, especially around Koh Bon West Ridge

Manta ray sightings at Koh Bon's West Ridge peak February through April, with some encounters across the wider season. A coral bommie at West Ridge is a known cleaning station, so keep your distance and don't sit on top of it or the mantas will move on.

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Practical information

Dive prices in Similan Islands

• Day trips from Khao Lak: ~4,500–5,600 THB ($125–$155 USD) for 2 dives. Park fees are usually added on top.
• 3-day, 3-night liveaboard: From ~18,400 THB ($510 USD), 11 dives included
• 4-day, 4-night liveaboard: From ~22,600 THB ($625 USD), 14 dives included
• National park fees: 500 THB park entry plus a 200 THB per-diving-day surcharge for divers. Liveaboards face a different fee structure (typically 900 THB entry plus 200/day). Always confirmed separately by your operator.

Getting to Similan Islands

The main gateway is Phuket International Airport (HKT). From there it's a 1- to 1.5-hour transfer by minibus north to Khao Lak, where most boats depart. Day-trip speedboats run from Thap Lamu pier and take 60 to 90 minutes to reach the islands depending on which site you're diving. Liveaboards leave from the same pier on overnight schedules.

You can dive the Similans on day trips from Phuket, but it adds 1.5 to 2.5 hours of land transfer each way to the same boat ride. That makes for a 14-plus hour day. Khao Lak is the more sensible base if Similan diving is the priority.