Photo: NEOM / Unsplash
Similan Islands
The Similan Islands are a chain of nine granite islands in the Andaman Sea, roughly 60km northwest of Khao Lak in southwest Thailand. The signature diving is topographic: house-sized granite boulders stacked into swim-throughs, channels and archways on the west sides of the islands, with sloping hard-coral reefs on the sheltered east. Most itineraries push north beyond the Similans proper to Koh Bon and Koh Tachai — the region's most reliable manta sites — and on to Richelieu Rock in the Surin park, Thailand's best-known whale-shark and manta pinnacle. The whole area sits inside two national parks (Mu Ko Similan and Mu Ko Surin) that close for the southwest monsoon: the parks are open only 15 October to 15 May and shut the rest of the year. Access is by boat from Thap Lamu (Khao Lak) or Tab Lamu-area piers, either as a long day trip or, for the northern sites, a 3-6 day liveaboard. Conditions range from easy reef dives to strong current and 40m boulder mazes, so the region spans open-water reef diving up to advanced-only pinnacles. Visibility is often 20-30m in the dry season but drops during the plankton blooms that bring the big animals. Whale sharks and mantas are never guaranteed and are most likely February to April.
What makes it special
- Granite boulder swim-throughs, channels and archways on the west sides — Elephant Head Rock is the best-known maze
- Richelieu Rock, a horseshoe pinnacle in the Surin park, is Thailand's most reliable whale-shark and manta site
- Koh Bon and Koh Tachai draw reef mantas to cleaning stations, most often in the dry season
- Iconic resting Indo-Pacific leopard (zebra) sharks on the sandy patches between reefs
Price range
$$–$$$
Trip length
1–6 days
Diver level
Open water
Trip type
Liveaboard, Day trip
Price is per person for a typical trip, excluding international flights ($$ $2,000–4,000 to $$$ over $4,000).
Similan day trips from Khao Lak run roughly 4,950-5,800 THB (about $135-160) for two dives, gear and park fees extra. Liveaboards typically run 3-6 days; a 4-day/4-night boat commonly costs about $825-965+ per person depending on cabin. National park fees are paid separately in cash: 500 THB park entrance plus a 200 THB/day diving surcharge, so a day trip is about 700 THB and a 4-day trip crossing both the Similan and Surin parks is roughly 1,800-2,300 THB per person.
Best time to dive
- Current
- Moderate
- Water temp
- 28–30.5°C (coldest Jan, warmest Apr)
- Visibility
- 10–30m — Commonly 20-30m in the dry season (December-April) when seas are calm. Drops to 10-15m during the plankton blooms of February-April that draw whale sharks and mantas — the big animals and the best visibility don't always coincide.
- Getting there
- Moderate — Reachable but with some friction: a 1.5h boat crossing.
- Experience
- Sheltered east-side reefs (Anita's Reef, East of Eden) suit Open Water divers. The signature deep boulder mazes and pinnacles — Elephant Head, Koh Bon ridge, Koh Tachai plateau, Richelieu Rock — carry stronger, shifting currents to 40m and are best for Advanced Open Water divers with good buoyancy. Most liveaboards recommend Advanced plus some logged experience.
Nearest airports
- HKT — Phuket International Airport (Main international airport; about 1-1.5 hours by road north to Khao Lak, where most liveaboards and day trips depart)
- TST — Trang / regional alternative (Minor domestic option; most divers route via Phuket (HKT) to Khao Lak. Boats board at Thap Lamu pier, near Khao Lak)
Permit required
Entry is inside Mu Ko Similan and Mu Ko Surin national parks; visiting and diving requires paying the park fees, collected in cash by operators at check-in.
Foreign adults: 500 THB park entrance plus a 200 THB per-day diving surcharge, per park. Day trip about 700 THB; a 4-day liveaboard entering both Similan and Surin parks about 1,800-2,300 THB. Paid in cash, separate from the trip price. (Base fee/surcharge structure per operator; confirm current amounts at booking.)
Marine life
Sightings are never guaranteed — the bars show typical likelihood by month.
| Month | Likelihood |
|---|---|
| January | occasional |
| February | occasional |
| March | occasional |
| April | occasional |
| May | occasional |
| June | occasional |
| July | occasional |
| August | occasional |
| September | occasional |
| October | occasional |
| November | occasional |
| December | occasional |
Napoleon (humphead) wrasse are regular visitors to the larger reef and boulder sites. IUCN Endangered; sightings are occasional, not guaranteed.
| Month | Likelihood |
|---|---|
| January | occasional |
| February | occasional |
| March | occasional |
| April | occasional |
| May | occasional |
| June | occasional |
| July | occasional |
| August | occasional |
| September | occasional |
| October | occasional |
| November | occasional |
| December | occasional |
Koh Bon and Koh Tachai are the main manta sites, with cleaning stations that reef mantas visit most often in the dry season; also seen at Richelieu Rock. Reported roughly January-May. Not guaranteed on any single dive.
| Month | Likelihood |
|---|---|
| January | rare |
| February | occasional |
| March | occasional |
| April | occasional |
| May | rare |
| June | rare |
| July | rare |
| August | rare |
| September | rare |
| October | rare |
| November | rare |
| December | rare |
Most reliably encountered at Richelieu Rock, and occasionally Koh Tachai/Koh Bon. Best odds February-April when plankton blooms peak. Genuinely unpredictable — many trips see none. Not present in the closed months (mid-May to mid-October).
| Month | Likelihood |
|---|---|
| January | occasional |
| February | occasional |
| March | occasional |
| April | occasional |
| May | occasional |
| June | occasional |
| July | occasional |
| August | occasional |
| September | occasional |
| October | occasional |
| November | occasional |
| December | occasional |
Reported at boulder sites such as Boulder City/Shark Fin Reef, often in loose groups. Present through the open season; sightings vary by site.
| Month | Likelihood |
|---|---|
| January | occasional |
| February | occasional |
| March | occasional |
| April | occasional |
| May | occasional |
| June | occasional |
| July | occasional |
| August | occasional |
| September | occasional |
| October | occasional |
| November | occasional |
| December | occasional |
One of two resident sea turtles in the Similans, seen on hard-coral reefs such as East of Eden. Present year-round on the reefs but only observable in the open season.
| Month | Likelihood |
|---|---|
| January | occasional |
| February | occasional |
| March | occasional |
| April | occasional |
| May | occasional |
| June | occasional |
| July | occasional |
| August | occasional |
| September | occasional |
| October | occasional |
| November | occasional |
| December | occasional |
Great barracuda and schooling chevron barracuda are common at pinnacle sites like Koh Tachai and Richelieu Rock. Present through the open season.
| Month | Likelihood |
|---|---|
| January | occasional |
| February | occasional |
| March | occasional |
| April | occasional |
| May | occasional |
| June | occasional |
| July | occasional |
| August | occasional |
| September | occasional |
| October | occasional |
| November | occasional |
| December | occasional |
Among the more commonly encountered sharks in the Similans, often resting on sand near reef edges through the open season. Sightings vary day to day. Not present during the mid-May to mid-October park closure.
| Month | Likelihood |
|---|---|
| January | occasional |
| February | occasional |
| March | occasional |
| April | occasional |
| May | occasional |
| June | occasional |
| July | occasional |
| August | occasional |
| September | occasional |
| October | occasional |
| November | occasional |
| December | occasional |
Seen on shallow reefs and around the islands; a common Andaman reef shark. Sightings vary by site and day through the open season.
| Month | Likelihood |
|---|---|
| January | occasional |
| February | occasional |
| March | occasional |
| April | occasional |
| May | occasional |
| June | occasional |
| July | occasional |
| August | occasional |
| September | occasional |
| October | occasional |
| November | occasional |
| December | occasional |
The second resident turtle in the park, seen grazing on reef flats. Sightings are frequent but not guaranteed on any given dive.
| Month | Likelihood |
|---|---|
| January | rare |
| February | rare |
| March | rare |
| April | rare |
| May | rare |
| June | rare |
| July | rare |
| August | rare |
| September | rare |
| October | rare |
| November | rare |
| December | rare |
A macro sighting that depends on the guide spotting it against matching crinoids or corals; most associated with Richelieu Rock. Open season only.
| Month | Likelihood |
|---|---|
| January | rare |
| February | rare |
| March | rare |
| April | rare |
| May | rare |
| June | rare |
| July | rare |
| August | rare |
| September | rare |
| October | rare |
| November | rare |
| December | rare |
A macro find rather than a reliable sighting — depends on a sharp-eyed guide, mainly at Richelieu Rock and similar sites. Present in the open season only.
| Month | Likelihood |
|---|---|
| January | occasional |
| February | occasional |
| March | occasional |
| April | occasional |
| May | occasional |
| June | occasional |
| July | occasional |
| August | occasional |
| September | occasional |
| October | occasional |
| November | occasional |
| December | occasional |
Common on the reefs and boulder sites, including Christmas Point; juveniles seen fairly often. Resident on Andaman reefs through the open season.
Dive sites
Worth knowing before you book
- The parks close completely for the southwest monsoon: no diving 16 May to 14 October each year, so the whole region is a mid-October-to-mid-May destination only.
- Whale sharks and mantas are the headline draw but are genuinely unpredictable — best odds February-April, and many trips see neither.
- The February-April period that brings the big animals also brings plankton that can cut visibility to 10-15m.
- Popular sites get crowded in high season; day-trip boats from Khao Lak can put many divers on the same reef at once, and Koh Tachai island itself has been closed to landing since 2016 to reduce pressure.
- The best sites (Koh Bon, Koh Tachai, Richelieu) carry strong, shifting currents at depth and realistically need Advanced-level experience, not entry-level certification.
Sources & last checked
Checked July 2026
This is a researched draft, not yet human-verified. The seasonality and logistics are drawn from the sources below — confirm specifics (permits, fees, closures) with an operator before you book.
- Mu Ko Similan National Park — fees and season — Thai National Parks
- Similan and Surin islands shut for five-month annual closure — The Nation Thailand
- National park fees for scuba diving at the Similan Islands — Similan Diving Tours
- Richelieu Rock, Andaman Sea — Dive The World
- Sea water temperature Similan Islands — seatemperature.info
- Find the Similan Islands Location | Ferry, Speedboat & Tour Options — Phuket-Tickets
- How to get to Similan Islands — Travelfish
Note on the data: Park closure (open 15 Oct - 15 May) is strongly corroborated across Thai news and operator sources. Coordinates and bounding box are approximate island-level positions, not surveyed GPS; the box is drawn to include the northern liveaboard circuit up to Richelieu Rock in the Surin park. Park-fee amounts (500 THB + 200 THB/day) come from operator fee pages and may have changed; flagged for verification against a current DNP source. Water temperature: Bands are +/-0.5C around the source's published monthly averages; the Andaman Sea stays warm (28-30C) year-round, though the park is only open 15 Oct-15 May so summer figures are off-season. Occasional cold-water upwellings during the season can drop a single dive several degrees below these surface averages. Access: Phuket (HKT) is ~1-1.5h by road to the Thap Lamu / Khao Lak piers, then a ~1-1.5h speedboat crossing to the Similans; day trip or 3-6 day liveaboard, with the northern sites (Koh Tachai, Richelieu Rock) an additional run beyond the islands. Independently verified 2026-07-20 (confidence high).