Diving in Thailand: Koh Tao, Phuket and the Similan Islands

Best season

Gulf: Mar–Sep · Andaman: Nov–Apr

Water temp

27–30 °C

Visibility

10–30 m

Difficulty

Easy to moderate

Beginners

Excellent (Koh Tao)

Open Water

~11,000–13,000 THB

Thailand has two coasts with opposite monsoon seasons: the Gulf of Thailand (Koh Tao, Koh Samui, Koh Phangan) and the Andaman Sea (Phuket, Koh Lanta, Khao Lak, the Similan and Surin islands). That means there's good diving somewhere in Thailand all year.

Koh Tao: the learn-to-dive capital

This small island in the Gulf of Thailand has dozens of dive centres and certifies tens of thousands of new divers each year. Why it's so popular:

• Some of the cheapest Open Water courses in the world, often with discounted accommodation
• Many calm, shallow bays and sites just 10–30 minutes by boat
• Warm water (28–30 °C) all year
• A fun, social atmosphere with lots of other new divers

Top sites: Chumphon Pinnacle and Sail Rock (between Koh Tao and Koh Phangan). These are granite pinnacles with huge schools of barracuda, batfish and trevally, and whale sharks in some seasons (often around March–May and September–October, but never guaranteed). Other sites: Japanese Gardens, Twins, White Rock, Shark Island, and the HTMS Sattakut wreck (about 18–30 m).

Best time: generally March–September. October to December brings the northeast monsoon with rain, waves and lower visibility, with November usually the wettest month.

Phuket and the Andaman coast

Phuket is a major base for day trips and liveaboards. Popular day-trip sites include:

• Racha Yai and Racha Noi: easy, clear bays (Racha Yai) and more advanced sites (Racha Noi) with occasional mantas.
• Shark Point, Anemone Reef, and the King Cruiser wreck: a sunken car ferry at about 12–32 m.
• Koh Phi Phi: famous islands with reef sites, blacktip reef sharks in shallow bays, and busy tourism.
• Koh Lanta (Hin Daeng and Hin Muang): deep pinnacles with soft corals; mantas and whale sharks sometimes; for experienced divers.

Best time: roughly November–April. May–October is the southwest monsoon, with rougher seas and fewer trips.

The Similan and Surin Islands

The Similan Islands National Park, about 70 km off Khao Lak, has giant granite boulders, swim-throughs, clear blue water and rich coral. Most people visit on liveaboards of 3–5 days, often combined with Koh Bon and Koh Tachai (manta rays) and Richelieu Rock in the Surin Islands, one of Thailand's most famous sites (whale sharks possible, plus seahorses, harlequin shrimp and more).

Season: the national park is usually open from mid-October to mid-May, with exact dates announced each year. Some sites have visitor limits and closures for reef recovery.

Level: Open Water divers can join many Similan liveaboards, but some sites have currents. Advanced certification and Nitrox are recommended. See liveaboards.

What you'll see

• Big schools of barracuda, trevally, batfish and fusiliers
• Whale sharks (seasonal, luck needed) and manta rays (Andaman, Koh Bon/Tachai)
• Turtles, moray eels, blue-spotted rays, octopus, cuttlefish
• Macro life: nudibranchs, seahorses, ghost pipefish, harlequin shrimp
• Blacktip reef sharks in shallow water

Typical prices (2026)

• Open Water course on Koh Tao: about 11,000–13,000 THB (roughly US$320–380), often with some accommodation included
• Fun dives Koh Tao: about 1,000–1,200 THB per dive; cheaper in packages
• Phuket day trip (2–3 dives): about 3,500–5,500 THB
• Similan liveaboard (3–4 days): about 20,000–40,000 THB, plus national park fees

Practical tips

• Choose the coast according to season (use our calendar)
• A 3 mm suit or even a rash guard is enough for most people
• Bring reef-safe sunscreen; some Thai marine parks ban harmful ingredients
• Motorbike accidents are a common cause of injury for travellers. Get proper insurance and be careful

Frequently asked questions

Is Koh Tao good for learning to dive?

Yes, it's one of the most popular places in the world to learn, thanks to low prices, warm calm water and many sheltered training sites.

When is the best time to dive in Thailand?

The Gulf (Koh Tao) is best around March–September; the Andaman Sea (Phuket, Similans) is best around November–April.

Can I see whale sharks in Thailand?

Yes, sometimes, particularly at Chumphon Pinnacle, Sail Rock and Richelieu Rock, but sightings are never guaranteed.