Similan Islands

Similan Islands — Andaman Sea, Thailand

The Similan Islands are nine uninhabited granite islands in the Andaman Sea, 70–100 km northwest of Phuket, forming part of the Mu Ko Similan National Marine Park. Since the park was established in 1982, the islands have become the centrepiece of Thailand's Andaman liveaboard diving season — operating November through April, closed during the monsoon months when the sea state makes access impossible.

The Topography

The Similans sit on the Thai–Myanmar Ridge, a granitic shelf that creates a distinctive diving environment: massive boulder formations that break the seafloor into canyons, overhangs, and swim-throughs alternating with hard-coral plateaus. The eastern faces of the islands are sheltered and shallow (5–20m) with gardens of branching coral and high fish density. The western faces are exposed, deeper, and more current-swept, with larger formations and better pelagic action.

Island 9 (Koh Bangu) and Elephant Head Rock (Ko Hua Chang) are consistently rated the best sites in the park — the boulder formations at Elephant Head create a labyrinth of arches and passages that rewards slow, exploratory diving.

The Marine Life

The Similans have been effectively protected since 1982 and the reef health reflects the decades of management. Giant trevally patrol the seamount tops. Leopard sharks rest on sand patches at 15–25 meters between the boulders. Hawksbill turtles feed in the shallow coral gardens. Whale sharks appear at the Similans from February through April, with sightings concentrated around the northern islands (8 and 9) where plankton concentrations are highest.

Richelieu Rock, technically within the Surin Islands rather than the Similans, is usually included on Similan itineraries as an extension site — and is often the highlight of the trip.

Liveaboard Season

The Similan season runs November through April. Liveaboards depart from Khao Lak (the closest port) or Phuket, with itineraries ranging from 3 nights (Similans only) to 7+ nights (Similans, Surin Islands, and Richelieu Rock). Book well in advance — October departures for the prime February–March window are in demand.

Practical Info

• Depth: 5–35m | Difficulty: Intermediate — variable current on western exposures; some exposed sites for advanced divers
• Access: Liveaboard from Khao Lak or Phuket; season November–April
• Best season: February–April for peak conditions and whale shark season
• Marine life: Whale sharks, leopard sharks, hawksbill turtles, giant trevally, Napoleon wrasse, schooling fusiliers