Thailand – Similan & Surin

Mu Ko Similan National Park lies about 70 km off Khao Lak in the Andaman Sea. Its nine numbered granite islands are lined with sheltered coral slopes on the east side and huge boulder fields with swim-throughs on the west. Koh Bon and Koh Tachai, added to the park in 1998, are the area's manta spots. Further north, Mu Ko Surin National Park has some of Thailand's richest hard-coral reefs and includes Richelieu Rock, a horseshoe-shaped pinnacle best known for whale sharks and macro life. Most diving is done from liveaboards out of Khao Lak, Thap Lamu, Khuraburi and Phuket, with speedboat day trips from Khao Lak. Both parks close every year during the south-west monsoon.

Facts

Best season: Mid-October to mid-May (dry north-east monsoon). Liveaboards mainly run November–early May; February–April usually brings the calmest seas and the best whale-shark chances
Annual park closure: Similan and Surin national parks close for the south-west monsoon, roughly 15/16 May to 14/15 October (2026–27 season: open 15 Oct 2026 – 15 May 2027). Exact dates are set by the DNP each year and may change with weather — check current dates
Park fees (foreigners): THB 500 entry per adult per national park (children less), plus a daily activity fee of THB 200 per diver per day; Similan and Surin are charged separately, so a 5-day north trip costs about THB 2,200–2,500 in park fees. Usually collected by the operator — check current fees
Visitor quota: Mu Ko Similan admits 3,850 visitors a day, of which 525 places are for scuba divers; tickets are electronic and overnight stays on the islands have been banned since 2018
Koh Tachai: The island itself has been closed to landings since 2016; the surrounding dive sites (Tachai Pinnacle) are still dived, and day-trip operators say snorkelling is no longer allowed there — check current rules
Water temperature: 26–29 °C most of the season, up to 30 °C at the surface; thermoclines can briefly drop it to about 25 °C
Visibility: Typically 20–40 m at the Similans; plankton blooms (often March–April) can reduce it but bring mantas and whale sharks. Coastal wrecks off Khao Lak are much murkier
Getting there: Fly to Phuket (HKT), then about 1–1.5 h by road to Khao Lak. Similan boats leave from Thap Lamu pier near Khao Lak; northern trips to Surin and Richelieu Rock often use Khuraburi pier (about 1 h 40 min from Khao Lak). Some liveaboards depart from Phuket or Ranong
Currents: Gentle on most east-coast Similan reefs; often strong and sometimes down-going on the west-side boulder sites, Koh Bon, Koh Tachai and the deep pinnacles, where negative entries are common

Season

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

The national park is open officially from 15 October to 15 May and closed during the southwest monsoon. December–February has the clearest water, March–April a good compromise, October still has swell.

Dive sites (31)

Similan North (islands 5–9)

Anita's Reef – 5–30 m, beginner
Beacon Reef – 5–40 m, intermediate
Breakfast Bend – 5–34 m, beginner
Christmas Point – 8–40 m, intermediate
Deep Six – 5–40 m, intermediate
Donald Duck Bay – 20 m, beginner
East of Eden – 5–40 m, beginner
Elephant Head Rock – 5–40 m, advanced
Hideaway – 7–35 m, beginner
North Point – 8–35 m, intermediate
Three Trees – 5–35 m, beginner
Tuna Wreck – 28–40 m, advanced
Turtle Rock – 8–25 m, beginner
West of Eden – 5–35 m, beginner

Richelieu Rock & Surin Islands

Ao Mae Yai – beginner
Hin Kong – 5–30 m, advanced
Koh Chi – 3–22 m, intermediate
Koh Pachumba – 3–18 m, beginner
Koh Torinla – 3–30 m, intermediate
Richelieu Rock – 3–35 m, intermediate
South East Point – intermediate
Turtle Ledge – 25 m, beginner

Khao Lak coast

Boonsung Wreck – 11–20 m, beginner
Premchai Wreck – 12–22 m, beginner
Sea Chart 1 – 22–40 m, advanced

Similan South (islands 1–4)

Boulder City – 5–35 m, advanced
Chinese Wall – 5–30 m, intermediate
Sharkfin Reef – 5–35 m, intermediate

Koh Bon & Koh Tachai

Koh Bon Pinnacle – 18–45 m, advanced
Koh Bon West Ridge – 10–40 m, intermediate
Tachai Pinnacle – 12–40 m, advanced

Operators (7)

Manta Queen Fleet (Khao Lak Scuba Adventures) – liveaboard, Khuk Khak, Khao Lak
Sea Dragon Dive Center – dive centre, Khao Lak
Khao Lak Explorer – dive centre, Khao Lak
Sea Bees Diving – dive centre, Khao Lak and Phuket
The Junk – liveaboard, Phuket
Thailand Aggressor – liveaboard, Phuket region (north itinerary from Andaman Sea Sun Travel Pier)
Dolphin Queen (Similan Diving Safaris) – liveaboard, Khao Lak

Routes (6)

Site positions are approximate and for orientation only — never for navigation. Island numbering differs between sources (the park counts Ko Hin Pousar as island 7, while many dive operators call Ko Payu island 7). Park opening dates, quotas and fees change every season; confirm them with your operator.