Diving in Thailand

Thailand dives on two coasts that run opposite seasons, and that split, not a province or a province list, is what actually decides a trip. Similan, Surin and Richelieu Rock, on the Andaman side out of Khao Lak, are the flagship: granite boulder islands and one soft-coral pinnacle reached at full coverage only by liveaboard, closed completely from mid-May to mid-October, and named by divers who have also dived the Philippines as the one Thai stop that holds up against it. A reef manta cleaning station at Koh Bon draws steady traffic. Crowding is the flip side of that reputation, and not only here: independent posts dated 2016, 2024 and 2025 all name Similan, Krabi's day-boat sites and Koh Tao alike as fought over, liveaboards included, jostling for space at anchor.

Phi Phi and Koh Lanta answer the same coast without the liveaboard commitment. Phi Phi dives year-round instead of closing for the monsoon, and its case is the paired Bida Islands: a near-guaranteed leopard or blacktip reef shark on a beginner-friendly wall. Koh Lanta reaches a comparable pelagic dive on a day boat instead: Hin Daeng and Hin Muang, a red- and purple-coral pinnacle pair carrying the Andaman's best oceanic manta chance outside a liveaboard, paired on the same trip with a gentler limestone cavern system at Koh Haa.

The Gulf side works on a different logic. Koh Tao trades site spectacle for volume and price, widely described as one of the busiest certification hubs anywhere, and its own headline dive, Sail Rock, splits opinion the way Richelieu Rock does further north: some days crystal clear with whale sharks overhead, others a murky pass with almost nothing to show. East along the same coast, Koh Chang adds a newer, smaller wreck dive: HTMS Chang, deliberately scuttled on 22 November 2012 onto a sandy seabed close to 30 m, its own deck running shallower at roughly 23 to 27 m.

Every Thailand trip settles one fact before the coast split: which season you are travelling in. The Andaman coast is best October to April and closes its flagship park completely from 15/16 May to 15 October, a date the park's own regional office reconfirms every year, never fixing it once for all. The Gulf runs roughly May to September on the standard telling, though Koh Tao markets itself as diveable year-round from sheltered bays. National-park entrance fees apply per visit, separate from any operator dive charge: Similan and Surin charge 500 THB for a foreign adult and 250 THB for a foreign child, and Phi Phi's own two-tier zone schedule adds up to around 600 THB for a first day's diving.

Certification works the same everywhere. The country's own CMAS-affiliated federation, ATUS, sits alongside PADI, SSI and the other international agencies, which still certify divers directly through their own dive centres. Hyperbaric chambers ask for proof of dive insurance before starting treatment, worth carrying regardless of what any park requires on paper. That treatment itself is available at only two points on the map: Phuket and Koh Tao run the country's confirmed recompression chambers, and Koh Samui is not a chamber location. Suvarnabhumi in Bangkok is the main international gateway, with Phuket, Surat Thani and Samui's own airport serving the Andaman and Gulf hubs; Khao Lak, the liveaboard departure town for Similan and Surin, sits roughly 100 km and 1.5 to 2.5 hours from Phuket airport by road. English is standard at dive operators in every hub.