Thailand

Diving in Similan Islands

42 sites82 species27–30 °C15–40 m vis

Photo: Stella Weis / Unsplash

The Similan Islands are Thailand's premier dive destination — nine granite islands in the Andaman Sea surrounded by schools of fish numbering in the thousands, resident manta ray populations at cleaning stations, and some of the most reliable whale shark encounters in Southeast Asia. With 40+ named dive sites spanning the inner islands, northern pinnacles, and the legendary Richelieu Rock, the Similans offer everything from gentle coral gardens for beginners to drift dives through boulder labyrinths for the experienced. The islands are composed of massive 200-million-year-old granite boulders that create Thailand's most distinctive underwater topography — swim-throughs, arches, caves, and cathedral-like chambers at sites like Elephant Head Rock and North Point. The park operates on a strict October–May season, closing entirely for five months during the southwest monsoon to allow reef recovery, making every dive here feel like a limited-edition experience. Accessible almost exclusively by liveaboard from Khao Lak, the Similan Islands deliver the full Andaman Sea diving fantasy: whale sharks at Richelieu Rock, manta ray cleaning stations at Koh Bon, leopard sharks resting on sandy channels, and some of the healthiest hard and soft coral gardens in Thai waters.

The name 'Similan' comes from the Malay word sembilan, meaning 'nine' — referring to the nine islands that form the archipelago.The Similan Islands are the exposed tops of a submerged mountain range, composed of massive granite boulders over 200 million years old.Richelieu Rock is considered the #1 dive site in Thailand and one of the most reliable places in the world to encounter whale sharks, with sightings reported almost weekly during peak season (February–April).The park closes annually from mid-May to mid-October during the southwest monsoon — a total of 5 months. This closure is critical for reef recovery and has helped maintain the Similans' world-class diving quality.Koh Bon Ridge is a premier manta ray cleaning station — resident manta rays visit the ridge year-round to have parasites removed by cleaner wrasse. Individual mantas can be recognized by their unique belly spot patterns.The Similan Islands are recognized as an Important Shark and Ray Area (ISRA) by the IUCN Shark Specialist Group, highlighting their global significance for shark and ray conservation.Island 8 (Ko Similan) features Donald Duck Bay — named because the shape of the granite boulders supposedly resembles Disney characters. It is the main drop-off point for day-trippers and the park headquarters.Schools of harlequin sweetlips numbering in the hundreds are a signature sight at Richelieu Rock, creating one of Thailand's most iconic underwater spectacles alongside massive schools of barracuda and trevally.A typical Similan liveaboard covers three distinct diving zones: the inner islands (Islands 1–9), the northern pinnacles (Koh Bon, Koh Tachai), and Richelieu Rock — each with completely different underwater character.The Similan Islands were named the 6th best diving destination in the world by Scuba Diving magazine's 2024 Readers' Choice Awards.

Explore the map

Select a pin to learn more. Use the zoom buttons or pinch to zoom.

Loading map…

Places on this map (14)

42 places have no verified map location yet. Browse the page lists for more places.

Conditions

Water temp

27–30 °C

Visibility

15–40 m

Depth

2–40 m

Current

Moderate

Best season

Jan–Apr (NE monsoon: calm seas, peak visibility 25–40m, best for whale sharks and manta rays)

Month	Summary
Jan	Peak season with 25–40m visibility and calm seas. Manta rays frequent Koh Bon Ridge and Koh Tachai Pinnacle. Leopard sharks rest on sandy channels throughout the inner islands. Whale sharks possible at Richelieu Rock.
Feb	Peak whale shark month at Richelieu Rock with sightings reported weekly. Visibility 25–40m. Manta ray cleaning stations active at Koh Bon and Koh Tachai. Best month for combining big-animal encounters with excellent photography conditions.
Mar	Whale shark peak continues at Richelieu Rock. Visibility 20–35m. Manta rays still present at northern pinnacles. Sea temperatures warm to 28–29°C. Last month of guaranteed calm before transition.
Apr	Tail end of whale shark season — still good encounters at Richelieu Rock. Visibility 20–30m. Manta rays remain at Koh Bon. Warmer water 28–30°C. Turtle nesting activity near season end. Quieter as low-season approaches.
May	First half of May: last chance before park closure. Visibility 15–25m with transition conditions. Manta rays and reef sharks still active. Warmer water 29–30°C. Fewer boats, more solitude. Park closes mid-May for monsoon.
Jun	Park CLOSED — southwest monsoon. No diving or tourism permitted. Reef recovery period. Best month for planning next season's trip and booking early-bird liveaboard deals for October reopening.
Jul	Park CLOSED — southwest monsoon continues. Heavy rainfall and rough seas. Coral spawning events occur naturally during this period. Reef ecosystems regenerate without diver pressure.
Aug	Park CLOSED — peak monsoon month. Strongest winds and heaviest rainfall. Nutrient-rich upwelling builds plankton blooms that will feed the coming season's manta ray and whale shark aggregations.
Sep	Park CLOSED — monsoon begins to ease toward month end. Operators prepare vessels and equipment for October reopening. Last chance for early-bird booking discounts before season starts.
Oct	Park REOPENS mid-October. Visibility 15–25m — improving through the month. Manta rays return to Koh Bon cleaning stations. Reef fish abundant after 5-month rest. Fewer divers, excellent value. Some sites still limited by residual swell.
Nov	Transition month with improving conditions. Visibility 20–30m. NE monsoon establishes, calming seas. Manta rays active at Koh Bon and Koh Tachai. Whale sharks begin appearing at Richelieu Rock. Great month for value before peak-season crowds.
Dec	Dry season in full swing with 25–35m visibility. Calm seas, sunny skies. Manta rays resident at northern pinnacles. Leopard sharks return to sandy channels. Eagle rays and reef sharks throughout the islands. Holiday season brings more liveaboards — book early.

Dive Sites (42)

Beacon Point (Koh Payu East)

5–25m · Beginner

Leopard shark sightings · Coral slope · Sandy channels

Christmas Point

5–30m · Beginner

Coral-encrusted boulders · Eastern aspect · Reef sharks

Coral Reef (Koh Pa Yang East)

3–18m · Beginner

Coral garden · Staghorn coral · Table coral

Deep Six

8–35m · Advanced

Boulder field · Swim-throughs · Macro life

Donald Duck Bay (Ao Luk)

1–8m · Beginner

Granite boulder beach · Snorkeling · Turtle encounters

Elephant Head Rock (Hin Pusa)

3–35m · Advanced

Granite boulder labyrinth · Swim-throughs · Tunnels and arches

Fantasy Reef (Koh Pa Yan West)

10–35m · Advanced

Granite boulders · Pelagic action · Deep wall

Garden of Eden

3–25m · Beginner

Mixed boulder and coral · Turtle encounters · Milder currents

+34more sites in the appGet the app →

Marine Life (82)

must-see

Great Hammerhead

must-see

Spotted Eagle Ray

must-see

Green Sea Turtle

must-see

Hawksbill Turtle

must-see

Atlantic Bottlenose Dolphin

must-see

Bull Shark

must-see

Loggerhead Turtle

must-see

Multibarred Angelfish

Common Lionfish

Great Barracuda

Striated Cone

Sickle Butterflyfish

Top 8 Dive Sites in the Similan Islands, Thailand

From whale sharks at Richelieu Rock to manta rays at Koh Bon. The 8 best dive sites in Thailand's Similan Islands ranked by marine life, conditions, and skill level.

10 min read

Similan Islands Diving Guide: 42 Sites Across 9 Granite Islands

Whale sharks at Richelieu Rock, manta rays at Koh Bon, and granite boulder labyrinths at Elephant Head. Complete guide to diving Thailand's Similan Islands.

7 min read

Similan Islands Conditions Guide: Seasons, Visibility, and Currents

27–30°C water, 15–40m visibility, and strong drift currents on the west side. Everything you need to know about diving conditions in the Similan Islands month by month.

12 min read