Thailand’s reefs sit in a small area with a large reputation: on the order of 148 km² of reef in the Andaman and the Gulf, 300+ hard-coral species, thousands of fish, a food web that still feeds towns and dive boats. They are also bleached, trampled, and loved to death. Closures, visitor caps, nurseries, and mooring buoys are the response, not a vibe.
Season is half the ecology. Mu Ko Similan closed about 16 May–14 October 2026; open about 15 October–15 May. Foreigner adult park fee commonly ~500 THB; daily cap cited 3,850. Park permits, Which coast, Snorkel or dive.
Reef types
Fringing reefs grow off shores and in shallow water. Most Thai islands have them. They are the snorkel you can walk into — and the first to take runoff, sewage, and fins.
Patch reefs rise from sand or rock offshore. Chumphon Pinnacle, Sail Rock, Hin Daeng are patch systems on topography. This is where dive boats earn the fuel.
Granite boulder reefs — Similans and Ko Tao. Swim-throughs, overhangs, hard and soft coral on rock. Complexity is the habitat.
Where the coral actually is
Andaman
Similan — nine granite islands. East: gentler gardens. West: boulder architecture. Visibility commonly 25 m+ in November–May. Staghorn, table, brain, massive Porites, fans and whips.
Surin — shallower, hard-coral flats that run hundreds of metres in 1–3 m of water. Arguably the best snorkel in the country when the park is open.
Hin Daeng / Hin Muang — pinnacles south of Lanta. Hin Muang (“Purple Rock”) is named for soft coral. Mantas, whale sharks, drift. Not a first dive.
Phi Phi — hammered by boats, still colourful. Maya Bay’s reef recovered during the 2018–2022 closure; reopening came with no swimming in the bay, no boats in the bay, caps.
Gulf
Ko Tao — fringing reefs around the island. Japanese Gardens, Mango Bay, Aow Leuk, Hin Wong: beginner depth, clownfish, wrasse, butterflyfish, grouper. Also the global PADI factory, which is a pressure.
Sail Rock — monolith between Phangan and Tao. Chimney swim-through, soft-coral walls, seasonal whale sharks. The Gulf’s serious site.
Ang Thong — 42 limestone islands west of Samui. Less dive infrastructure, better rest.
Bleaching
When water stays above about 30.5 °C, corals expel zooxanthellae and go white. Stay hot, they die.
| Year | Severity | What people measured |
|---|---|---|
| 2010 | Severe | Andaman shallow hard coral losses often cited 50–80%; branching worst |
| 2016 | Moderate–severe | Global event; Surin flats hit |
| 2020 | Localised | Some recovery from 2016 |
| 2024 | Severe | Indian Ocean heat; both coasts; damage still being counted |
Recovery can take 5–15 years if other stresses (sediment, sewage, fins, anchors) drop. Massive Porites is the heat-tougher seed bank. Branching coral is the pretty stuff that dies first.
Climate zones. El Niño years raise bleaching risk. That is not a reason to skip the country; it is a reason not to stand on the coral.
What Thailand actually did
Seasonal closures — Similan and Surin shut mid-May to mid-October. Five months without fins. Unusual globally; it shows in the gardens.
Maya Bay model — closed 2018–2022. Reopened with no swim, no boats in the bay, 300 at a time / 1 hour style caps (confirm the current board). Blacktips returned during the quiet.
Nurseries — fragments on frames, then outplant. Phuket, Tao, Similans.
Ko Tao operators — self-policing culture, debris dives, mooring buoys. Save Koh Tao coordinates. Still a lot of Open Water students in 3 m of water.
Open Water courses commonly £200–250 and 3 days — verify with the shop. More PADI cards come out of Tao than anywhere else, which is a boast and a carrying-capacity problem.
Snorkel versus tanks
Many of the best gardens are 1–5 m. Mask, snorkel, fins. Surin, Lipe’s Walking Street trail, Tao’s Japanese Gardens, Ang Thong.
A mask you own — adult snorkel mask — beats a rental fog factory. Rash vest instead of a chemical you will rinse onto the coral. Dry bag for the boat. Water shoes if you must enter over rubble — still do not walk on live coral.
Do not feed fish. Do not grab turtles. Do not drone a marine park. Park permits.
Gateway boats and airports: Getting there, Phuket, Koh Samui.
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Snorkel or dive, Dive sites, Which coast, Park permits, Marine life.