Thailand – Koh Tao & Samui

Koh Tao, a small granite island in the western Gulf of Thailand, is one of the busiest places in the world to learn to dive: dozens of schools run two boat trips a day to sites only minutes from Mae Haad and Sairee. Sheltered bays and boulder reefs suit beginners, while offshore pinnacles such as Chumphon, Southwest and Sail Rock (between Koh Tao and Koh Pha Ngan) draw big schools of barracuda, trevally and batfish and, in season, whale sharks. Three navy ships scuttled as artificial reefs add wreck dives. Koh Samui and Koh Pha Ngan operators run day trips to the same pinnacles and to the Ang Thong archipelago. The Gulf has its own monsoon rhythm: Koh Tao dives all year, and the wettest, roughest months are November–December – the opposite of the Andaman coast.

Facts

Best season: Year-round on Koh Tao; calmest and clearest roughly January–May and again in September–October. June–August brings south-west winds (east-coast sites are used). November–December is the wet north-east monsoon with lower visibility – diving continues on the sheltered west side. The opposite of the Andaman coast.
Whale sharks: Possible all year but most often March–May, with fairly regular sightings again in September–October (Sail Rock, Chumphon Pinnacle, Southwest Pinnacle, Shark Island); never guaranteed
Water temperature: About 27–30 °C most of the year, around 28 °C in the November–December monsoon; occasional thermoclines on deeper sites
Visibility: Typically 10–30 m, best on offshore pinnacles in calm months; reduced by plankton and by rain run-off in November–December
Getting there: Lomprayah high-speed catamaran (and other ferries, incl. a night boat) from Chumphon to Koh Tao; or fly to Koh Samui (USM, Bangkok Airways) and take the catamaran via Koh Pha Ngan. Surat Thani → Koh Tao by ferry takes about 3 h with stops on Samui and Pha Ngan. Check current timetables.
Fees: Koh Tao lies outside the national-park network; since April 2022 the municipality charges a 20 THB visitor fee for reef and waste conservation. Koh Nang Yuan (privately owned) charges about 250 THB per adult to land; Mu Ko Ang Thong NP about 300 THB for foreign adults. Check current fees.
Seasonal closure: Mu Ko Ang Thong National Park usually closes about 1 November – 15 December for the monsoon (weather-dependent); Koh Tao itself has no closure. Check current dates.
Dive scene: Koh Tao is a high-volume training hub (Open Water to instructor and tech); boats run morning and afternoon two-dive trips, groups are typically max. 4 divers per guide

Season

Best months: Feb, Mar, Apr, May, Jun, Jul, Aug, Sep
Acceptable: Jan, Oct
Poor: Nov, Dec
Water temperature: 27–30 °C

The Gulf of Thailand is best from February to September. The northeast monsoon brings the worst weather in November and December, with visibility sometimes under 5 m. Whale sharks are most often seen March to May (Chumphon Pinnacle, Sail Rock).

Dive sites (37)

Koh Tao east & south

Aow Leuk – 4–18 m, beginner
Hin Wong Pinnacle – 10–30 m, intermediate
HTMS Hanhaksattru – 18–24 m, intermediate
King Kong Rock – 5–22 m, beginner
Laem Thian – 2–20 m, intermediate
Lighthouse Bay – 4–18 m, beginner
Lighthouse Pinnacle – 5–30 m, intermediate
Shark Island – 3–24 m, advanced
Tanote Bay – 2–18 m, beginner

Offshore pinnacles

Chumphon Pinnacle – 14–36 m, advanced
Samran Pinnacle – 9–28 m, advanced
Southwest Pinnacle – 5–30 m, advanced

Koh Tao west & north

Ghost Fleet – 28–35 m, advanced
HTMS Sattakut – 18–30 m, advanced
Junkyard – 7–12 m, beginner
Mango Bay – 2–15 m, beginner
Pottery & Three Rocks – 3–14 m, beginner
Sairee Reef – 3–12 m, beginner
Unicorn Wreck – 38–50 m, advanced
White Rock – 5–22 m, beginner

Koh Nang Yuan

Green Rock – 4–28 m, intermediate
Japanese Gardens – 1–14 m, beginner
No Name Pinnacle – 18–30 m, advanced
Red Rock – 2–21 m, intermediate
Twins – 5–18 m, beginner

Sail Rock & Koh Pha Ngan

Haad Yao – 16 m, beginner
Khom Beach – beginner
Ko Tae Nai – 7 m, beginner
Koh Kong Yai – 20 m, intermediate
Koh Ma – 0–20 m, beginner
Sail Rock – 5–40 m, intermediate

Chumphon coast

Hin Lak Ngam – 5–25 m, intermediate
HTMS Prab – 24 m, intermediate
Koh Ngam Noi – 16 m, intermediate

Koh Samui & Ang Thong

Koh Madsum – beginner
Koh Wao – 20 m, beginner
Koh Yippon – 18 m, beginner

Operators (12)

Big Blue Diving – dive centre, Sairee, Koh Tao
Crystal Dive – dive centre, Mae Haad, Koh Tao
Ban's Diving Resort – resort, Sairee Beach, Koh Tao
Roctopus Dive – dive centre, Sairee, Koh Tao
Simple Life Divers – dive centre, Koh Tao
Master Divers – dive centre, Mae Haad, Koh Tao
Easy Divers – dive centre, Lamai Beach, Koh Samui
100 Degrees East – dive centre, Koh Samui
Haad Yao Divers – dive centre, Haad Yao, Koh Pha Ngan
Sensui Dive Center – dive centre, Chumphon town
Davy Jones' Locker (DJL Diving) – dive centre, Sairee, Koh Tao
Coral Grand Divers – dive centre, Sairee Beach (north end), Koh Tao

Routes (10)

Site positions are approximate unless marked otherwise and are for orientation only — never for navigation. Several Koh Tao sites are placed from published descriptions rather than GPS. Dive with a local operator; conditions change with wind direction and season.