Thailand's Similan Islands: A Complete Dive Guide

The Similan Islands represent Thailand's diving crown jewel — a national marine park closed half the year to protect it, and spectacular the half it's open. Add the nearby Surin Islands and Richelieu Rock, and you have one of Asia's premier liveaboard routes.

The Geography

Nine granite islands (plus additional sites) form the Similan chain, roughly 70km offshore from Khao Lak. The islands themselves are stunning — white sand beaches, jungle interiors, and massive granite boulders both above and below the waterline.

Further north, the Surin Islands and legendary Richelieu Rock extend the diving range.

The Signature Sites

Richelieu Rock

Thailand's most famous dive site, and for good reason. This submerged pinnacle in open water attracts everything — whale sharks during season, manta rays, dense schools of barracuda and trevally, and macro life that keeps photographers occupied between megafauna appearances.

It's not always on — some days it's quiet. But when Richelieu fires, nothing in Thailand compares.

Koh Bon

A reliable manta cleaning station. The western ridge drops away into blue water where mantas come to be cleaned by wrasse. Patient divers on the sand at 20-25 metres often get extended encounters.

Koh Tachai

Before its closure to camping (the island was being loved to death), Koh Tachai Pinnacle was already legendary. The diving remains exceptional — a granite pinnacle surrounded by soft corals with strong fish life and frequent leopard shark sightings.

The Similans Proper

The numbered islands (4-9) offer diverse diving: boulder formations creating swim-throughs and caverns, hard coral gardens, and reef life in abundance. Less dramatic than Richelieu but excellent for variety.

Surin Islands

Known for snorkeling with whale sharks (when present) and softer, more relaxed diving. The Surin sites offer a break from the current-swept pinnacles to the south.

Conditions

• Season: November to May only (park closed June-October)
• Water temperature: 27-30°C
• Visibility: 15-40m, best February-April
• Currents: Variable; can be strong at exposed sites

When to Go

November-January: Season opening, water still warming, whale sharks beginning to appear

February-April: Peak season, best visibility, highest chance of whale sharks and mantas, busiest boats

May: Season closing, quieter boats, conditions still good

Whale sharks are most reliably seen February-April, particularly around Richelieu Rock.

What You Need

• Certification: Open Water sufficient for most sites
• Experience: Comfortable intermediate divers will enjoy everything
• Current skills: Helpful but not demanding by global standards

Liveaboard vs Day Trips

Day trips from Khao Lak reach the closer Similan sites. Liveaboards are essential for Richelieu, Koh Bon, and the full experience. The crossing takes hours — sleeping aboard means more diving, less travelling.

Most Similan liveaboards run 4-night itineraries covering the full route from Similans through Surin to Richelieu.

The Value Proposition

Thailand offers exceptional value in Asian diving. Quality liveaboards cost less than comparable boats elsewhere. The diving rivals anywhere in the region for reef health and big animal potential.

For divers seeking accessible, affordable, genuinely excellent diving without expedition logistics, the Similans deliver.

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