Best Dive Sites in Thailand: From Koh Tao to the Similans

Thailand's diving is split between the Gulf of Thailand (east coast) and the Andaman Sea (west coast) — two bodies of water with distinct characteristics, different peak seasons, and different marine life. The Gulf is generally calmer, more accessible year-round, and home to Koh Tao, which certifies more divers than almost anywhere on earth due to its shallow, visibility-clear training sites. The Andaman offers larger, more dramatic dive sites including the world-class Similan Islands and Richelieu Rock, often cited as one of the top five dive sites on earth.

Koh Tao's best sites include Chumphon Pinnacle (strong currents, large schools of fish, whale shark sightings possible), Southwest Pinnacle (coral-covered rocks with leopard sharks), and HTMS Sattakut (wreck dive, 30m). All three require Open Water certification minimum; Chumphon demands some experience with current diving. The Similan Islands (reachable by liveaboard from Khao Lak, open November–April) feature extraordinary visibility — often 30m — around granite boulder formations. Richelieu Rock in the Surin Islands is the jewel: a submerged pinnacle carpeted in soft corals and reliably visited by whale sharks from February to April. For budget accessible diving without a liveaboard, Koh Phi Phi's Bida Nok and Bida Noi sites off the southern tip have excellent coral gardens and blacktip reef sharks. Hin Daeng and Hin Muang, south of Koh Lanta, are considered the Andaman's best accessible sites with regular manta ray encounters.