Mergui Archipelago
Diving Mergui means entering Myanmar, and that is the first thing to settle. The country has been in armed conflict since the February 2021 coup. As of 4 August 2026 the UK FCDO advises against all but essential travel to the Myeik Archipelago and the islands south of Tanintharyi township, and against all travel to the rest of Tanintharyi Region. Trips are still running: Master Liveaboards and The Smiling Seahorse both list Mergui departures on sale through 2027 and beyond. They leave from Ranong in Thailand, clear Myanmar immigration at Kawthaung, and carry Myanmar government permits — a $50 visa plus roughly $350 in park and port fees on a 10-night trip, paid to a state run by the military. That money is not neutral, and the decision belongs to the diver. The diving is remote expedition diving, not resort diving. Black Rock is the reason people go: 276 oceanic manta encounters have been logged there and at the neighbouring Twins since 2011, 216 of them photo-identified as individual animals, with Black Rock alone accounting for over 95% of the area's manta sightings. Western Rocky and Shark Cave have swim-through tunnels that historically held tawny nurse sharks. The macro is real — ghost pipefish, seahorses, and the Ranong guitarfish, a Bay of Bengal endemic that has been found resting in groups on deep sand at Black Rock in some Decembers and Januaries. Visibility is the honest weak point at 5–40m and often 10–20m, noticeably worse than the Similans a few hours south. The plankton that clouds the water is what feeds the mantas. Season runs roughly November to April, with the calmest, clearest conditions December to April.
What makes it special
- Black Rock: 276 oceanic manta encounters logged since 2011, 216 individuals photo-identified, and over 95% of the area's manta sightings at this one islet (IUCN SSC Shark Specialist Group ISRA factsheet, 2024)
- Ranong guitarfish, a Bay of Bengal endemic, recorded resting in groups of 5–20 on sand at 25–30m at Black Rock and North Twin in positive Indian Ocean Dipole years
- Swim-through tunnels at Western Rocky and Shark Cave — the Shark Cave cavern starts at 5m, drops to 16m and runs about 20m through the islet
- Photo-ID has tracked 23 individual mantas moving between Black Rock and the Twins and Thai sites including the Similans, Koh Lanta and Hin Daeng/Hin Muang
Price range
$$–$$$
Trip length
6–11 days
Diver level
Advanced open water
Trip type
Liveaboard
Price is per person for a typical trip, excluding international flights ($$ $2,000–4,000 to $$$ over $4,000).
Master Liveaboards lists Mergui 10-night trips at roughly $2,625–3,950 per person depending on season and cabin, excluding flights. On top of that are obligatory surcharges: a $50 Myanmar visa and about $350 in park entrance and port fees for a 10-night itinerary, so budget roughly $400 per person in government fees. Shorter 8-day itineraries from Ranong-based operators sit lower. There is no land-based or day-trip alternative.
Best time to dive
- Current
- Strong
- Water temp
- 24–30°C (coldest Jan, warmest Apr)
- Visibility
- 5–40m — Published range is 5–40m and it genuinely spans that. Expect 10–20m on many dives. The Andaman's nutrient load and large-amplitude internal waves are what cut visibility — and what bring the mantas in.
- Getting there
- Demanding — Liveaboard only, with a 10h open-ocean crossing to reach the diving.
- Experience
- Operators require Advanced Open Water and a minimum of about 30 logged dives, and expect comfort in current. Black Rock produces strong down-currents, Shark Cave and Stewart Island get heavy surge, and the tunnels at Western Rocky and Shark Cave are overhead environments. Nitrox is strongly recommended for the repetitive deep profiles.
Nearest airports
- HKT — Phuket International Airport (Nearest international airport. Operators run shared road transfers of roughly 5–6 hours north to Ranong on embarkation day; Thai exit formalities are done at Ranong immigration.)
- UNN — Ranong Airport (Domestic Thai airport, served from Bangkok; about 30–40 minutes from Ranong port, the usual departure point for Mergui liveaboards.)
- KAW — Kawthaung Airport (Domestic Myanmar airport at the border town where liveaboards clear Myanmar immigration; almost never used by divers, who arrive by boat from Ranong.)
Permit required
Myanmar government permits are arranged by the liveaboard operator, not by the diver. Boats depart Ranong in Thailand, complete Thai exit formalities, then cross to Kawthaung where Myanmar immigration officers board the vessel for entry screening. A $50 Myanmar visa is mandatory. Permit conditions and cruising areas are set by the Myanmar authorities and can change at short notice.
About $350 per person in park entrance and port fees on a 10-night itinerary (Master Liveaboards), plus the $50 Myanmar visa. These are paid to Myanmar government agencies.
Marine life
Sightings are never guaranteed — the bars show typical likelihood by month.
| Month | Likelihood |
|---|---|
| January | occasional |
| February | peak season |
| March | peak season |
| April | occasional |
| May | occasional |
| June | rare |
| July | rare |
| August | rare |
| September | rare |
| October | rare |
| November | rare |
| December | rare |
Black Rock is the site. Scientific dive surveys and citizen-science submissions logged 276 encounters across Black Rock and the Twins since 2011, with 216 individuals photo-identified and up to 28 in a single day; over 95% of those were at Black Rock. Operators report mantas from late January to early May with the best odds in February and March. Blank dives are common — this is not a guaranteed encounter, and the published numbers cover fourteen years of effort, not a single season.
| 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 |
Listed as a supporting species in the ISRA factsheet and reported occasionally at Western Rocky and the outer sites. There is no documented whale shark season for Mergui — encounters track the same plankton-rich late-season window that brings the mantas. Treat any operator whale shark claim as a chance encounter.
| Month | Likelihood |
|---|---|
| January | rare |
| February | occasional |
| March | occasional |
| April | rare |
| May | rare |
| June | rare |
| July | rare |
| August | rare |
| September | rare |
| October | rare |
| November | rare |
| December | rare |
Mobula thurstoni is a supporting species for the Black Rock & the Twins ISRA. Devil rays pass Black Rock in the same late-season window as the oceanic mantas and are easy to misidentify from a distance. Encounters are brief fly-bys rather than cleaning-station time.
| 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 in the blue at Shark Cave, Black Rock and the Banks. Numbers are modest by Indo-Pacific standards; this is a fished archipelago and reef shark encounters are singles and pairs rather than schools.
| 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 |
Indo-Pacific leopard shark, Stegostoma tigrinum, listed as a supporting species for the Black Rock & the Twins ISRA. Usually resting on sand at the base of slopes at Black Rock, North Twin and Fan Forest Pinnacle. Population is Endangered across its range and numbers here reflect that.
| Month | Likelihood |
|---|---|
| January | occasional |
| February | rare |
| March | rare |
| April | rare |
| May | rare |
| June | rare |
| July | rare |
| August | rare |
| September | rare |
| October | rare |
| November | rare |
| December | occasional |
Sightings appear tied to the positive phase of the Indian Ocean Dipole rather than to a fixed season. Documented dive observations are from December 2019, January 2020, March 2020, February 2023 and December 2023. In an IOD-neutral or negative year, expect nothing. Deep — the aggregations sit at 25–30m at the base of the slope.
| 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 |
The Burma Banks were famous for silvertips in the 1990s, when baited encounters with numbers of large animals were routine. Fishing pressure has thinned them and few itineraries still make the 125km run west. Code this as a long shot on an unusual itinerary, not a Mergui highlight.
| 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 |
Aetobatus ocellatus, a supporting species in the ISRA factsheet. Reported at North Twin, Black Rock and the deeper slopes, usually in passing along the drop-offs.
| 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 Andaman nurse shark is Nebrius ferrugineus, not the Atlantic species. Western Rocky's tunnel is the best chance and animals of around 3m have been reported there. Shark Cave was named for them and they are now rarely seen at that site; Stewart Island's juveniles are also much less dependable than older trip reports suggest.
| 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 |
Reliable enough among the gorgonians at Fan Forest Pinnacle and on the walls at Shark Cave that guides look for them on most itineraries. Sightings track the dive season simply because nobody is in the water outside it.
| 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 |
Seahorses are reported on the sea fans and rubble at Shark Cave and Fan Forest Pinnacle. Operator accounts rarely identify to species, so treat the tigertail attribution as the likely Andaman species rather than a confirmed record. A guide who knows the site is the difference between seeing one and not.
| 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 |
A supporting species for the Black Rock & the Twins ISRA and the most frequently seen shark on the reefs, usually resting under ledges at Fan Forest Pinnacle, Shark Cave and Black Rock.
Dive sites
Worth knowing before you book
- Myanmar has been in armed conflict since the February 2021 military coup. As of 4 August 2026 the FCDO advises against all but essential travel to the Myeik Archipelago and against all travel to the surrounding Tanintharyi Region, warns the conflict is increasingly volatile, and notes the military regime can introduce travel restrictions at any time. Travelling against that advice can invalidate travel insurance.
- The permits are paid to the junta. A Mergui trip costs roughly $400 per person in Myanmar government visa, park and port fees, paid to a state run by the military. Tourist money in Myanmar is not neutral. Divers should book with that fact in front of them, or not book.
- Visibility is the weak point. Published range is 5–40m; 10–20m is common, and it is noticeably worse than the Similan or Surin Islands a few hours south in Thailand.
- Mantas are not reliable. Research effort concentrated encounters at Black Rock between late January and early May, best around February and March, and boats still run multiple dives there without a sighting. Whale sharks are a chance encounter, not a season. Treat operator claims of reliable mantas as marketing.
- Sites are named for animals that have thinned out. Shark Cave's nurse sharks are now rarely seen, and the Burma Banks silvertip aggregations that built the region's reputation in the 1990s have been heavily fished. Gillnet fishing continues near Black Rock — a pregnant Ranong guitarfish was documented as bycatch there in February 2023.
Sources & last checked
Checked August 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.
- Myanmar travel advice: regional risks — UK Foreign, Commonwealth & Development Office
- Myanmar travel advice: warnings and insurance — UK Foreign, Commonwealth & Development Office
- Black Rock & the Twins ISRA Factsheet — IUCN SSC Shark Specialist Group
- Mergui Archipelago 10 nights — Master Liveaboards
- The Mergui Archipelago — The Smiling Seahorse
- Diving in Burma (Myanmar) - Mergui Archipelago — Dive The World
- Burma Mergui - The Manta Ray Paradise — Dive The World
- Three Islets / Shark Cave - Burma / Myanmar — IDC Phuket
- Myeik water temperature — Seatemperature.info
Note on the data: Confidence is low deliberately, and the reason is the operating status. Liveaboards appear to be running — Master Liveaboards lists Mergui departures with prices and mandatory fees through 2027–2029, and The Smiling Seahorse lists 2026–2028 expeditions — but that rests entirely on two operator booking pages, which have a marketing incentive and can advertise departures that do not sail. No independent 2025–2026 confirmation of an actual completed Mergui trip was found, and Myanmar permit conditions can change at short notice. The security picture is primary-sourced: FCDO advice fetched 2026, last updated 4 August 2026, placing the archipelago and islands under 'all but essential travel' while the rest of Tanintharyi Region is 'all travel'. Australian Smartraveller was attempted three times and timed out each time, so only one government advisory is cited. Manta biology, the Ranong guitarfish and the supporting shark and ray list come from the IUCN SSC Shark Specialist Group ISRA factsheet (2024), which is the strongest source here; manta month-by-month seasonality comes from an operator blog and is coded conservatively as a result. Site coordinates are approximations derived from published distances and bearings from Kawthaung and from island positions, not surveyed dive-site GPS — treat them as island-level. Shark Cave and Three Islets are the same site and are entered once. Water temperature is interpolated; see waterTempNotes. The statement that permit money reaches a military-controlled government rests on the fee structure (Myanmar government visa plus government park and port fees) combined with FCDO's description of a military regime, not on a fetched financial audit. Water temperature: Interpolated, not measured at the dive sites. maxC follows the monthly coastal climatology for Myeik (27.8–30.6°C) trimmed toward the 26–30°C range dive operators publish for the offshore islands; minC is lowered to reflect thermoclines, since the Andaman's large-amplitude internal waves drive temperature mixing at these islets (ISRA factsheet) and divers report cooler water below the thermocline at Black Rock. Access: Liveaboard-only in practice: from Phuket, the nearest international airport, it is a shared road transfer of roughly 5–6 hours to Ranong, then Thai exit formalities, a short boat crossing to Kawthaung for Myanmar immigration, and an overnight steam of about 10 hours or more to reach the outer sites — Black Rock sits roughly 160km northwest of Kawthaung.