Koh Rong Archipelago
The Koh Rong archipelago sits about 25km off Sihanoukville in the Gulf of Thailand, and it is a marginal dive destination that is honest about being one. Visibility is the defining limitation: the gulf here is shallow, silty and fed by mainland runoff, so inshore sites around Koh Rong, Koh Rong Sanloem and Koh Koun average roughly 10m and range from 5m to 25m depending on wind and rain. Depths are shallow too, mostly 6-18m, which makes the area a workable place to learn but a thin one for experienced divers. Marine life is modest: nudibranchs, seahorses, cuttlefish, moray eels, scorpionfish, stingrays and reef fish, with blacktip reef sharks turning up occasionally at the outer sites. There are no reliable large pelagics. Coral cover is patchy and the wider area has been depleted by bottom trawling, which Cambodian law bans in water shallower than 20m but which NGOs and local press report continuing inside the protected zone. The better diving is offshore at Koh Tang and Koh Prins, roughly 50-80km out, where visibility runs 10-30m and reef structure is more developed - but reaching them means a 4-5 hour dive-boat crossing from Sihanoukville and usually an overnight trip. Season matters and runs opposite to Thailand's Andaman coast: the southwest monsoon brings rain and rough seas from about mid-May to early October, and the calmer, clearer window is roughly November to April.
What makes it special
- Among the cheapest places in Southeast Asia to certify - a PADI Open Water course runs roughly $400-450 including boat trips and food
- Offshore Koh Tang and Koh Prins group, 50-80km out, with 10-30m visibility and blacktip reef sharks at Shark Point, reached on overnight boat trips
- A documented seahorse hotspot: Marine Conservation Cambodia has recorded six Hippocampus species at a single island in the Koh Rong archipelago
- Koh Tang was the site of the 1975 Mayaguez incident, the last ground battle involving US forces in the Vietnam War
Price range
$
Trip length
3–7 days
Diver level
Open water
Trip type
Land based, Day trip, Liveaboard
Price is per person for a typical trip, excluding international flights ($ = under $2,000).
Cheap by dive-travel standards. Scuba Nation on Koh Rong Sanloem lists a two-dive day trip at about $95 including equipment, lunch and boat, a Discover Scuba day at about $110, and snorkelling at about $30; PADI Open Water has been quoted around $445. Overnight Koh Tang trips have been reported around $275-335 per person and Koh Prins around $325, including boat, food and dives. Ferries from Sihanoukville run about $13-17 each way. No marine park fee is charged to divers. Prices are operator-published and change; confirm before booking.
Best time to dive
- Current
- Mild
- Water temp
- 26–33°C (coldest Jan, warmest Apr)
- Visibility
- 5–25m — Inshore sites around Koh Rong, Koh Rong Sanloem and Koh Koun run 5-25m and average about 10m; 5m days are normal after rain or wind. Offshore at Koh Tang and Koh Prins it improves to roughly 10-30m, typically about 20m. Worst during the southwest monsoon, June to September.
- Getting there
- Moderate — Reachable but with some friction: a 4.5h boat crossing.
- Experience
- Most sites are 6-18m with mild current and suit newly certified divers - this is primarily a training and casual fun-diving area. A few sites (Cobia Point, and the walls and drift dives at Koh Prins that reach 30m+) are better with Advanced Open Water. The offshore Koh Tang and Koh Prins trips are open to certified Open Water divers but involve a long small-boat crossing.
Nearest airports
- KOS — Sihanouk International Airport (Regional flights from Phnom Penh, Bangkok, Ho Chi Minh City and several Chinese cities; roughly 30 minutes by road to the Sihanoukville ferry pier)
- PNH — Phnom Penh International Airport (Cambodia's main international airport; about 4-5 hours by road or bus to Sihanoukville, or a short domestic hop to KOS)
Marine life
Sightings are never guaranteed — the bars show typical likelihood by month.
| 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 |
Treat operator claims with caution. Several Cambodian dive pages advertise whale sharks at Shark Point 'in December and May', but no research, tracking or photo-ID source corroborates a Gulf of Thailand aggregation off Cambodia. Encounters here are chance events, not a season, and no month override is coded because no credible seasonality was found.
| 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 |
Rays are among the more reliable sightings on the sand flats, especially at Koh Tang's Stingray Alley and the Koh Prins sand sites. Operator reports say 'stingrays' generically, so the species mix is not confirmed.
| 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 |
Moray eels are routine on the rocky inshore reefs, and Koh Prins has a site named Moray Eel Parade for the number of species on one sand-and-rock stretch. Species-level identification is not documented.
| 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 around the offshore Koh Prins sites and at Sponge Garden inshore, more often in the dry season when water is clearer.
| 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 |
Reported at Koh Moan North and a site named Eagle-ray Alley in the Koh Prins group, both on multi-day offshore trips. Not seen inshore around Koh Rong.
| Month | Likelihood |
|---|---|
| January | commonly seen |
| February | commonly seen |
| March | commonly seen |
| April | commonly seen |
| May | commonly seen |
| June | commonly seen |
| July | commonly seen |
| August | commonly seen |
| September | commonly seen |
| October | commonly seen |
| November | commonly seen |
| December | commonly seen |
Found year-round in the anemone patches at Two Tone Garden, Koh Koun and Koh Prins' Anemone Garden.
| 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 mainly at the offshore Koh Prins and Koh Tang sites, including a cleaning station at Shark Point. Inshore sightings around Koh Rong are much less frequent. Claim rests on operator pages 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 |
Reported year-round at Cobia Point and Sponge Garden off Koh Rong Sanloem. Sightings are not seasonal but are not guaranteed on any given dive.
| Month | Likelihood |
|---|---|
| January | commonly seen |
| February | commonly seen |
| March | commonly seen |
| April | commonly seen |
| May | commonly seen |
| June | commonly seen |
| July | commonly seen |
| August | commonly seen |
| September | commonly seen |
| October | commonly seen |
| November | commonly seen |
| December | commonly seen |
Present year-round on the rocky reefs and sponge slopes around Koh Rong Sanloem.
| Month | Likelihood |
|---|---|
| January | commonly seen |
| February | commonly seen |
| March | commonly seen |
| April | commonly seen |
| May | commonly seen |
| June | commonly seen |
| July | commonly seen |
| August | commonly seen |
| September | commonly seen |
| October | commonly seen |
| November | commonly seen |
| December | commonly seen |
The most reliable thing to look at here. Nudibranchs are found year-round on the shallow rocky reefs off Koh Rong and Koh Rong Sanloem, with one site named for them.
| 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 |
Cuttlefish are reported year-round on the shallow Koh Rong Sanloem and Koh Koun sites. Species identification on operator pages is generic 'cuttlefish'; S. pharaonis is the expected Gulf of Thailand species but has not been confirmed to species level here.
| 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 |
Marine Conservation Cambodia has recorded six Hippocampus species in Cambodian study areas including H. comes, and identified a seahorse hotspot at a small island in the Koh Rong archipelago. Most records come from seagrass and survey work rather than recreational dives, and finding one on a normal fun dive is unlikely.
Dive sites
Worth knowing before you book
- Visibility is the main problem, not a caveat. Inshore sites average around 10m and drop to 5m after rain or wind; the Gulf of Thailand here is shallow, silty and fed by mainland runoff.
- Marine life is modest and coral cover is patchy. Reef fish, nudibranchs, seahorses, cuttlefish and the occasional blacktip reef shark or ray - no reliable large pelagics. Operator claims of whale sharks in December and May are not corroborated by any research source.
- Protection exists on paper more than in the water. Bottom trawling is illegal in water under 20m and the archipelago has been a Marine Fisheries Management Area since 2016, but NGOs and Cambodian press report illegal trawling continuing to damage seagrass and reef inside the zone.
- The best diving needs a 4-5 hour crossing. Koh Tang and Koh Prins are overnight or multi-day trips on small dive boats, weather-dependent and cancelled outright through the southwest monsoon.
- Sihanoukville itself is a hard sell. Large-scale casino and construction development from about 2017 brought sewage discharge, sedimentation and runoff, then a bust that left unfinished towers standing; the town is a transit point, not a destination.
- Seasonality is the reverse of Thailand's Andaman coast. June to September brings rough seas, rain and cancelled boats - divers arriving on a Thailand-style schedule get the worst of it.
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.
- Cambodia - Monsoonal, Tropical, Humid (Climate) — Encyclopaedia Britannica
- Anti-trawling Blocks Spark Marine Revival in Cambodia — CamboJA News
- Seahorses in Cambodia — Marine Conservation Cambodia
- Fishers left with no land, no fish, in fire sale of Cambodian coast — Mongabay
- Boom to bust for Cambodia's Chinese casino town — Asia Times
- Chinese Casino Pollutes Beach on Cambodian Island Near Sihanoukville — Radio Free Asia
- Koh Rong Sanloem dive sites — Scuba Nation Diving Centre
- Price List — Scuba Nation Diving Centre
- Koh Tang — Wikipedia
- Koh Rong (Cambodia) Water Temperature Today & Throughout the Year — Sea Temperature
- Sihanoukville to Koh Rong Samloem ferry times and prices — Direct Ferries
- Koh Tang Island List of Dive Sites for Scuba Diving — Private Scuba
- Koh Prins dive sites — Scuba Nation Diving Centre
Note on the data: Confidence is low on purpose. Dive-site depths, names and marine life rest almost entirely on operator pages (Scuba Nation / divecambodia.com, The Dive Shop Cambodia, Private Scuba) - Cambodia has no dive-tourism research literature and no fetched government page. Site coordinates are approximate island-level positions, not surveyed GPS; Koh Prins in particular is placed from a rough bearing and distance description and should be corrected. Marine Fisheries Management Area area (405 sq km, 2016) and national park status (2018) come from research and NGO summaries, not a fetched Fisheries Administration document. Monsoon timing is well corroborated (Britannica: southwest monsoon mid-May to early October) but per-month sea-state data was not found. Water temperature is from a commercial sea-temperature aggregator, not a met agency. Operator claims of whale sharks 'in December and May' at Shark Point are coded rare with a caveat and should be treated as unverified. The national-parks.org page for Koh Rong Marine National Park returned 403 and could not be read. Water temperature: Warm year-round, roughly 28-31C average, with the minC and maxC values here taken from the source's published monthly extremes rather than dive-depth measurements; a 3mm shorty or rash guard is normally enough. Access: Sihanouk International Airport (KOS) to the Sihanoukville ferry pier is about 30 minutes by road; the speed ferry to Koh Rong or Koh Rong Sanloem takes roughly 45 minutes to an hour, while the offshore Koh Tang and Koh Prins sites need a 4-5 hour dive-boat crossing from the mainland (about 2 hours from Koh Rong Sanloem to Koh Tang) and are dived as overnight trips.