Thailand – Koh Lanta & Krabi

Koh Lanta is the jump-off point for the southern Andaman's best-known open-water sites. Hin Daeng and Hin Muang, two isolated pinnacles far offshore, drop as steep walls covered in red and purple soft coral and are visited by manta rays and, in some seasons, whale sharks. Closer in, the small limestone group of Koh Haa offers a sheltered lagoon for beginners, cavern dives such as the Cathedral and the Chimney swim-through, while the twin Koh Rok islands are shallow, easy reef dives. From Ao Nang on the Krabi mainland, day boats visit the shallow islands of the bay, and Lanta-based centres also run trips south to the Trang islands. The Koh Phi Phi and Koh Bida sites are covered by the Phi Phi module.

Facts

Best season: November – April for calm seas and the best visibility; many Lanta centres run mid-October to mid-May and scale down in the south-west monsoon (roughly May/June – September). Some shops stay open all year with weather-dependent trips.
Water temperature: About 27–30 °C all year, warmest February – April
Visibility: Typically 15–30 m in high season; Hin Daeng/Hin Muang can exceed 30 m on good days, while monsoon months may drop to 5–15 m
Getting there: Fly to Krabi (KBV) or Trang (TST); from Krabi a shared van takes about 2.5 h. By road: car ferry from Baan Hua Hin to Koh Lanta Noi, then a bridge to Koh Lanta Yai. In high season boats run from Krabi, Ao Nang and Koh Phi Phi to Saladan pier.
National park fees: Koh Haa, Koh Rok and Hin Daeng/Hin Muang lie in Mu Ko Lanta National Park. Lanta dive centres charge a separate marine park fee of about 600 THB per foreign diver per day (park entrance alone is listed at 200 THB per foreign adult). Ao Nang bay islands: about 400 THB. Check current fees.
Seasonal closure: The park's outer islands close in the rainy season – commonly given as 16 May – 14 October, with Hin Daeng, Hin Muang and Koh Haa quoted by operators as closed 15 May – 15 October. Dates differ between sources (Koh Rok, for example, is also listed as closed only June – September), so check current dates.
Currents: Mild at Koh Rok and the Koh Haa lagoon; medium to strong at Hin Daeng and Hin Muang, where dives start and end on a descent line

Season

Best months: Nov, Dec, Jan, Feb, Mar, Apr
Acceptable: May, Oct
Poor: Jun, Jul, Aug, Sep
Water temperature: 28–30 °C

Best from November to April (December–February clearest and busiest). May to October is the southwest-monsoon low season: diving is possible but rougher with poorer visibility; sources differ on the edge months.

Dive sites (21)

Trang islands

Emerald Cave (Koh Mook) – beginner
Koh Kradan – 2–12 m, beginner
Koh Ngai – 8–16 m, beginner
Koh Waen Train Wreck – 5–30 m, intermediate

Hin Daeng & Hin Muang

Hin Daeng – 5–60 m, advanced
Hin Muang – 9–70 m, advanced

Koh Rok

Hin Ngam (Koh Rok) – 20 m, beginner
Koh Rok – 3–25 m, beginner
Lak Siam (Koh Rok) – 20 m, beginner

Koh Haa

Koh Haa #2 – 4–30 m, beginner
Koh Haa #3 – 3–18 m, beginner
Koh Haa #4 – 5–30 m, beginner
Koh Haa 1 (The Chimney) – 5–35 m, intermediate
Koh Haa 6 (Secret Garden) – 5–35 m, intermediate
Koh Haa Lagoon – 5–30 m, beginner
Koh Haa Yai – 3–35 m, intermediate

Koh Maa (between Lanta and Phi Phi)

Koh Maa Shipwreck Park – 12–30 m, beginner

Ao Nang (Krabi)

Koh Mae Urai – 4–20 m, beginner
Koh Poda – 3–12 m, beginner
Koh Si (Ao Nang) – 20 m, beginner
Koh Yawasam – 3–18 m, beginner

Operators (10)

Lanta Diver – dive centre, Saladan, Koh Lanta
Phoenix Divers Koh Lanta – dive centre, Saladan, Koh Lanta
Dive & Relax Koh Lanta – dive centre, Lanta Castaway Beach Resort, Long Beach, Koh Lanta
Blue Planet Divers – dive centre, Saladan boat terminal, Koh Lanta
Palm Beach Divers – dive centre, Saladan (Moo 3), Koh Lanta
Apo Dhatu Divers – dive centre, Klong Dao, Saladan, Koh Lanta
Kon-Tiki Krabi – dive centre, Ao Nang, Krabi
Aqua Vision Dive Company – dive centre, Sai Thai, Ao Nang, Krabi
Go Dive Lanta – dive centre, Saladan (6 Moo 1), Koh Lanta
Hidden Depths Diving – dive centre, Saladan, Koh Lanta

Routes (9)

Site positions are approximate and for orientation only — never for navigation. Park fees, closure dates and operating seasons change; confirm them with your dive centre. Hin Daeng and Hin Muang are deep, exposed open-water sites for experienced divers.