Koh Rong Sanloem

IslandsPreah Sihanouk,Cambodia

Fragile nature — stay on the trail, leave no trace.

A roadless Cambodian island of white sand and jungle hills where the sea flares blue-green around every stroke on a moonless night.

September·Quiet month

Jul–Oct

Full southwest monsoon: the wettest, greyest stretch, peaking in September (~518mm over 21 wet days). Rough seas delay or cancel ferries and dive trips, most often in September and October, and travellers thin to almost none — though many bungalows stay open at deep discounts.

Year-round White sand, warm 28-30°C shallows and jungle trails are here every day of the year. What the seasons change is how calm and how clear the sea is, and how brightly the plankton glows.

Koh Rong Sanloem is a Cambodian island where the sea lights up when you swim in it. Go in on a moonless night and blue-green sparks flare around every kick and stroke. By day the same water is clear and entirely ordinary. The island is a 9.5-kilometre ribbon of jungle-covered hills in the Gulf of Thailand, rising to 210 metres in the northwest, with no roads anywhere on it. Its eastern shore is Saracen Bay, a long crescent of powder-white sand where the shallows shade from turquoise to deep blue and shelve so gently that you can wade a long way out. There are no high-rise hotels — only coconut palms, wooden jetties and a scatter of low bungalows. A forest trail crosses the island from Saracen Bay to Sunset Beach in about thirty minutes, and the yellow-sand coves on that side are far emptier than the main bay. Electricity and internet arrive only in patches, so an evening here comes down to a hammock, a canoe and the sound of the waves. That is also what makes the glow work: there is almost no lamplight to compete with it. Wait for a new moon, wade in around midnight, and the plankton do the rest, scattering cold light off your arms while the real stars crowd the sky above. The light is there all year but shows best in the November-to-April dry season, when the sea lies calm and clear. In 2018 the whole island was folded into Koh Rong Marine National Park, protecting the reefs offshore and the forest that still covers the interior.

Worth knowing

Good to know

Time your swim to a new moon — the glow needs true darkness, so pick the nights around the new moon, choose a beach with no lamps, and wade in toward midnight when it peaks.
The sea is calmest from November to April — the dry-season months bring flat, clear water, ideal for snorkelling the reefs and for the calm crossings between beaches.
The glow shows best away from the lit main bay — Saracen Bay's jetties and bungalow lights wash out the plankton, so the sparks are brightest along a darker, unlit stretch of shore.
Cross to Sunset Beach or Lazy Beach for solitude — Saracen Bay holds the piers and bungalows, while a 30-minute jungle trek west reaches quieter coves and the island's best sunsets.
Bring a torch for the dark paths — the island runs on patchy power with no street lighting, so a flashlight helps you find the way between beach and bungalow after dark.

Things to do

1
Cross the island on foot to Sunset Beach
A forest trail runs from Saracen Bay over the ridge to the west shore in about thirty minutes. Sunset Beach faces open water rather than the ferry pier, and as the light drops the sky behind the coconut palms turns copper and pink. The crowd thins to a handful of long-stay travellers.
2
Paddle a kayak to the hidden coves
Push a kayak or canoe out from Saracen Bay and follow the shoreline to coves the trails never reach, where sandstone rocks meet clear water. With the island's coast running some 37 kilometres, there is always another empty beach around the next headland.
3
Look down over the island's two coasts
Climb to one of the island's hill viewpoints and both coasts open up at once — jungle-covered ridges on one side, Saracen Bay's pale crescent on the other, and the open Gulf beyond. From the beach the island feels far wider than it is; from up here you can see how little land there actually is.
4
Swim through the glowing plankton
On a dark, moonless night, walk into the sea and sweep your arms through the water: every movement sets off a spray of cold blue-green sparks around you. It is one of only a few places where the plankton glow this brightly, and floating in it feels like drifting through a field of slow stars.

Watch

Nearby

15 km