Richelieu Rock

Richelieu Rock — Surin Islands, Thailand

Richelieu Rock is a horseshoe-shaped submerged pinnacle — barely breaking the surface at low tide — sitting alone in the Andaman Sea about 20 km northeast of the Surin Islands, roughly 180 km north of Phuket. There is nothing remarkable about it above water. Below the surface, it is the most biodiverse dive site in Thailand, and one of the most celebrated in all of Southeast Asia.

What Makes It Extraordinary

The rock rises from 35 meters on the sandy surrounding floor and the walls are smothered in life — purple soft corals, whip corals, gorgonian sea fans, and clumps of bubble coral that expand in daylight. The volume of fish is exceptional for any single site: enormous schools of yellowtail fusiliers, chevron barracuda, batfish, and snappers orbit the pinnacle continuously.

But the macro life is what separates Richelieu from other Thai sites. The pinnacle hosts seahorses (Hippocampus kuda and H. comes) year-round, harlequin shrimps on the sea stars, Coleman's shrimps on fire urchins, ghost pipefish in the crinoids, and ornate ghost pipefish in the fans. Photographers who can resist the whale shark panic and stay small will find this is one of the great macro dives in Asia.

Whale Sharks

From February through April, whale sharks (Rhincodon typus) appear at Richelieu Rock with a frequency that makes it Thailand's most reliable whale shark site. They come to feed on the plankton bloom that descends on the rock in the northeast monsoon season. A typical encounter: the dive boat crew spots a whale shark feeding at the surface, divers drop in mid-water, and the animal continues on its path at 6–10 meters while you free-dive or snorkel parallel to it. Some encounters happen mid-dive, with the shark rising from the blue, circling the pinnacle once, and departing.

The Dive

Richelieu is typically done as a multi-circuit drift around the pinnacle at varying depths. Start deep (25–30m) and work shallower. The current runs around the rock from different directions depending on tidal stage — your guide will set the entry point. On the surface, the rock is small enough that you can always see the boat. At 15 meters you can circle the entire pinnacle in a few minutes, so pacing yourself to look slowly is the skill the site rewards.

Getting There

Richelieu Rock is liveaboard-only. The closest land is Koh Surin, and that's a national park with no dive infrastructure. Most Andaman Sea liveaboards departing from Khao Lak or Phuket include Richelieu Rock on their Similan/Surin itineraries (November–April season).

Practical Info

• Depth: 5–35m
• Difficulty: Intermediate — mild to moderate current
• Access: Liveaboard only; departures from Khao Lak or Phuket
• Best season: November–April (Andaman Sea liveaboard season)
• Whale shark season: February–April
• Marine life: Whale sharks, seahorses, ghost pipefish, harlequin shrimps, barracuda schools, fusiliers, batfish, gorgonian fans