8 Best Similan Islands Diving Sites and Trip Guide

Featured image: User: (WT-shared) Similanscuba at wts wikivoyage, Public domain, via Wikimedia Commons.

Similan diving at a glance: who it suits

Mu Ko Similan National Park is a seasonal marine park about 70 km west of Khao Lak, made up of nine main islands plus Koh Bon and Koh Tachai, which joined the park in 1998. Reefs on the east side slope gently and suit almost any certified diver. Boulders on the west side drop past 40 m and bring current, tunnels and arches. Outer pinnacles such as Koh Bon and Koh Tachai are mostly liveaboard territory. Site descriptions here are a starting point, not a promise of visibility, calm water or wildlife on your dates.

• Certified divers with a recent dive: west-side boulders and the outer pinnacles.
• Newly certified or rusty divers: east-side reefs, with a refresher if you have had a long gap.
• Non-certified travelers: a course with a qualified center, or snorkeling.
• Short on time: a two-dive day trip from Khao Lak.
• Chasing manta rays: a multi-day liveaboard in season.

When to dive the Similans: season and conditions

Operators report the diving season running from roughly October to May, with one listing giving 15 October to 15 May. Closing and opening dates shift each year, so read the current notice from the national park authority before booking. Our page on park opening dates tracks the pattern. February to April is widely described as the calmest stretch, with visibility reported anywhere from 15 m to 40 m depending on source. Sea temperature is quoted between 25 °C and 29 °C, and water temperature details help you choose a suit. Warm water is not a reason to skip exposure protection, so agree your suit and dive computer with the operator in advance.

Day trip or liveaboard for Similan diving

Prices and hours checked November 2026. Day trips and liveaboards reach different sites, so decide the format before the site. One Khao Lak operator runs a two-dive day trip for ฿5,400 per person, with lunch aboard. A full-day schedule from that operator runs like this: hotel pickup between 06:30 and 08:00, boarding at Tub Lamu Pier at 08:30, then about 1.5 hours by speedboat. Dives start at 10:30 and 14:00, and you are back at the pier near 17:00. Read day trip planning for the full routine. Phuket-based travelers should see Phuket departure options first.

8 Best Similan Islands Diving Sites, From Reefs to Pinnacles

Sites run from gentle east-side slopes to current-swept pinnacles. Conditions and rotations change by day and by boat, so treat each entry as typical rather than guaranteed.

1. Islands #4 and #5 east-side reefs

Koh Miang (#4) holds the park headquarters, and the small granite island of Koh Ha (#5) sits just east of it. Sheltered reefs slope from about 5 m to 30 m, with coral bommies, fusiliers and snappers on the way down. Turtles and blue-spotted rays are regular visitors, and blacktip reef sharks sometimes pass through.

Currents are mostly mild, so dives run long and relaxed, and guides pick the exact site on the day. Skip these reefs if you came for big boulders, because the swim-throughs sit on the outer edges.

2. Honeymoon Bay

Honeymoon Bay is shallow close to the island, then falls away as a steep sloping reef to about 30 m. Its shallows are used for training courses and night dives, which makes it a common first Similan dive for new divers. Current can run over the slope, so ask your guide about the plan before descending.

Snorkelers can also use the shallow part. Experienced divers wanting walls or boulder mazes will find it tame.

3. Elephant Rock

Elephant Rock lies between islands 7 and 8, named for a rock that resembles an elephant's head. Layers of granite form channels and swim-throughs, and early-morning dives often show crabs, sharks and big fish feeding. Trevally hunt small fish in the shallows.

Expect current, and plan it with a dive guide rather than solo. Skip it if you have only a handful of logged dives or are not comfortable with moving water.

4. Christmas Point

Christmas Point sits at the western corner of island 9 and shows what Similan boulder diving is about. Tidal currents have eroded rock into channels and swim-throughs. Coral gardens sit around 24 m, so check your depth and gas before going deeper along the rocks.

Tide runs fast in some conditions along the deep rock face. Newly certified divers should pass and choose an east-side reef instead.

5. Stonehenge

Stonehenge is at the northern tip of island 4, where many large boulders let you dive between them. A current is almost always running, which also feeds the soft corals. One Khao Lak day-trip schedule lists it on Thursdays, paired with West of Eden.

Good buoyancy and a recent dive are the entry ticket. Skip it if you want a calm, sheltered dive.

6. Koh Bon

Koh Bon lies north of the main Similan group and features a vertical wall with a sloping reef on its western side. Giant manta rays are reported feeding here during the October to May season, though sightings are never guaranteed. Currents are stronger than at most Similan sites, so it is mainly for advanced divers.

A deeper pinnacle in the bay is worth the short bottom times only in clear water and slack current. Not every boat visits it. Skip it if you need gentle conditions.

7. Koh Tachai

Koh Tachai is further north and is best known for a submerged, flat-topped pinnacle just off the island. Other options include rocky bays, a wall on the west side and a gentle coral slope to the south. Reported sightings include batfish, giant trevally, clown triggerfish and barracuda swirling in the blue.

One day-trip operator lists Tachai only on Saturdays, so liveaboards reach it far more often. Skip it if you are limited to a short day trip and want guaranteed access.

8. Richelieu Rock

Richelieu Rock is a horseshoe-shaped pinnacle that barely breaks the surface, with about 1 m showing at low tide. Operators put its maximum depth between roughly 35 m and 40 m, so confirm the planned depth with your guide. Purple soft corals and hundreds of anemones host several clownfish species, and ghost pipefish and seahorses are the macro targets.

Whale sharks and manta rays appear only occasionally, so do not book on that promise. It lies in Mu Ko Surin National Park, not the Similans. Skip it if you need a Similan-only itinerary.

Which Similan dive sites match your experience

Certification cards do not describe how comfortable you are with a boat entry, current or depth. Tell the center when you last dived and how many dives you have logged. Boat requirements also vary. One liveaboard program asks for certification to 30 m or an onboard upgrade, but that is one boat's rule, not a park rule.

Which park you are actually in: Similan versus Surin

Richelieu Rock lies in Mu Ko Surin National Park, which became a marine park in 1981. Many package titles say Similan while including Surin and Richelieu days. Park fees depend on which park you enter, so ask the operator for the day-by-day site list. Our Similan versus Surin comparison helps you pick between them.

Wildlife: what is realistic and when

Turtles, blue-spotted rays, fusiliers, snappers and moray eels are common on east-side reefs. Reef sharks and Napoleon wrasse turn up in the blue. Manta rays are reported at Koh Bon and Koh Tachai during the October to May season. Whale sharks are possible but unreliable, so read whale shark seasons before building a trip around one. Treat any claim of year-round sightings with caution. Dive descriptions are not guarantees.

What Similan diving costs: budget bands and hidden extras

Published rates are operator-specific. One Khao Lak shop lists a day trip at ฿5,400 per person, with a full gear set at ฿500, a dive computer at ฿300 per day and Nitrox at ฿300 per tank. Round-trip transfers from Phuket, Khok Kloy and Natai add ฿500 per person on that listing. A February 2027 liveaboard listing for 15 dives costs from ฿24,500 and adds gear at ฿500 per day, a computer at ฿200 per day and a night-dive flashlight at ฿150 per day. It also quotes ฿4,000 for an advanced course upgrade. Park entry is usually extra and varies by nationality and trip length.

• Park fee: usually excluded, ask which park it covers.
• Gear and dive computer rental: ask for sizes in advance.
• Nitrox: some boats include it for certified divers, others charge per tank.
• Transfers from Phuket: often a surcharge.
• Tips for crew and guides: usually excluded.
• Insurance: confirm the cover for the depths you plan to dive.
• Advanced upgrade course: separate cost.

Choosing an operator and a boat: safety checklist

Ask direct questions before you pay a deposit. A good operator answers each one without hedging.

• How many divers per guide?
• Is the dive plan flexible when current is strong?
• Is oxygen and first-aid equipment aboard?
• Is Nitrox available and analyzed?
• What state is the rental gear in?
• Which sites will you actually dive, in writing?
• What if you are not cleared for a planned dive?
• What are the weather and cancellation terms?

Mistakes to avoid on a Similan dive trip

Most problems come from assumptions made before the boat leaves.

• Booking a Similan trip that is mostly Surin and Richelieu without checking the itinerary.
• Assuming a beginner-friendly site means a beginner-friendly boat.
• Skipping a refresher after a long gap.
• Leaving exposure protection ashore because the water is warm.
• Booking a flight right after a liveaboard.

Not diving: snorkeling and non-diver companions

Companions can join some boats, but only if the product accepts non-divers with proper snorkeling stops and supervision. A snorkeling ticket is not a beginner scuba experience. Shallow bays such as Honeymoon Bay and east-side reefs suit swimmers. See Similan snorkeling options for companion-friendly choices.

Logistics: Khao Lak, Phuket, transfers and flights

Khao Lak day trips use hotel pickups between about 06:30 and 08:00, depending on your zone, then boarding at Tub Lamu Pier around 08:30. Phuket and Khok Kloy pickups sit around 07:00 on the same operator's listing. Liveaboards leave from a pier after a van transfer, so ask for the exact meeting time. Allow a no-fly interval after your final dive before any flight. Returning to the pier does not reset that clock.