Scuba diving & snorkeling in Thailand: best spots, certification, seasons & costs.

Two coasts, two dive seasons

Thailand straddles two seas, and that single fact governs almost everything about diving here. The Andaman Sea on the west — Phuket, Krabi, the Similan and Surin Islands — has the clearest water and the marquee sites, but it is exposed to the southwest monsoon, so its best diving is the dry season, roughly November to April. The Gulf of Thailand on the east — Koh Tao, Koh Samui, Pattaya — is calmer and diveable year-round, which makes it the fallback when the Andaman is rough. Learn to read the seasons and you can dive somewhere good in Thailand in any month. Our weather & seasons guide maps the wet and dry windows coast by coast.

The regions worth the trip

• Similan & Surin Islands (Andaman) — Thailand’s world-class sites: granite boulder swim-throughs, clear blue water and big pelagics. Reached by liveaboard from Khao Lak or Phuket; seasonal access only (the marine parks close in monsoon).
• Phuket & the Racha Islands — the most convenient Andaman base, with easy day-trip reefs and good schools; a short hop to Phi Phi and the King Cruiser wreck.
• Koh Phi Phi & Koh Lanta — postcard limestone scenery above water, reefs and the deep pinnacles of Hin Daeng & Hin Muang (manta and whale-shark territory in season) below.
• Koh Tao (Gulf) — the training island: warm, shallow, sheltered bays and dozens of dive schools. The default place to learn and to log cheap fun dives.
• Pattaya & Sattahip (Gulf) — the closest diving to Bangkok, with a cluster of wrecks and easy reefs ideal for a weekend without a flight.
• Koh Lipe (far south Andaman) — clear water and quiet reefs near the Malaysian border, best in the high season.

Getting certified — and why people fly to Koh Tao for it

To dive beyond a shallow guided taster you need an Open Water certification from PADI, SSI or an equivalent agency — a recognised, lifelong qualification. Koh Tao is famous for being one of the cheapest and highest-volume places in the world to earn it:

• Open Water course — ~4 days, typically 9,000–12,000 baht on Koh Tao including materials and certification, often with cheap accommodation bundled in. Somewhat higher on Phuket, Phi Phi or Lanta.
• Advanced Open Water — ~2 days, roughly 8,000–11,000 baht; unlocks deeper sites and skills like navigation and night diving.
• Discover Scuba (taster) — a single guided shallow dive for the uncertified, a few thousand baht; fun, but not a substitute for training.

Seasons & closures — the part people miss

• Andaman high season: roughly November–April, with the clearest water and best visibility around February–April. This is the window for Phuket, Phi Phi and liveaboards.
• Similan & Surin close annually: the marine national parks shut during the southwest monsoon, usually mid-May to mid-October, so liveaboards only run in the open months — book the season, not the week.
• Gulf year-round: Koh Tao and Pattaya dive all year and cover you when the Andaman is rough, though the Gulf sees more rain and softer visibility around October–December.

Marine-park sites also charge a national-park entry fee on top of your dive cost, with a higher foreigner rate that residents can often reduce — the same system explained in our national parks in Thailand guide.

What it costs

• Fun dives: around 1,000–1,800 baht per dive on a day trip, cheaper per dive on two- or three-dive trips; gear rental is often included or a small add-on.
• Liveaboards (Similans): the big-ticket item — typically 18,000–35,000 baht for a multi-day trip depending on boat and cabin.
• Courses: from ~9,000 baht (Open Water on Koh Tao) upward.
• Snorkel day trips: a modest group price including gear, guide and lunch.
• Park fees: add the marine-park entry fee where it applies (residents can often pay the Thai rate).

Safety & insurance — don’t skip this

Thailand has recompression chambers in the main dive regions (Phuket, Koh Samui and others), but they can be far from remote sites, so safety margins matter. Solid medical cover is essential either way — see our health insurance in Thailand guide for how dive and travel cover fit alongside a resident health plan.

Snorkeling — no certification needed

If you just want the reefs without the training, Thailand delivers. Koh Phi Phi, the Surin Islands, Koh Lipe, the Racha Islands and countless day-trip reefs offer easy, shallow snorkeling; operators run guided group trips with gear and lunch, and most resort beaches rent masks and fins. It’s the simplest way to see Thailand’s marine life on a free weekend — and a good way to decide whether you want to invest in learning to dive. For more weekend ideas near where you live, see things to do in Thailand.

Frequently asked