Parts of the sea around Koh Larn, off Pattaya in Thailand, appeared green on September 30, 2026. Reports say a plankton bloom after heavy rain is the likely explanation, but sampling was still underway and the final species identification had not been reported in coverage through October 2. The discoloration was not reported uniformly around the island.
Where the sea around Koh Larn turned green
The change was reported around Koh Larn, also written Ko Lan, a tourist island off Pattaya in Chonburi province, in the northern Gulf of Thailand. Pattaya Mail said the green color was especially visible near Tawaen Beach, but reports describe discoloration in sections rather than around the entire island. The available coverage does not establish comparative water-quality measurements for individual beaches.
Thairath English reported the suspected bloom and heavy rain on September 30. Pattaya Mail and Reuters, carried by Free Malaysia Today, published further reporting on October 1 and 2.
What likely caused the green water—and what is not confirmed
Local reports describe a plankton bloom following heavy rain and unsettled weather as the likely explanation. Runoff can carry freshwater, sediment and nutrients from land into coastal waters; plankton growth is also affected by nutrient levels, currents, temperature and weather. Those factors offer context, not proof of the cause in every affected stretch of Koh Larn.
Do these 3 things before closing this tab:
1Scan for outdated or missing drivers - takes under a minute2Clear out junk files and repair common Windows errors3Fix the driver behind crashes, sound loss and screen glitches#1 Best Overall
Reuters quoted Arvut Munhapon, a senior researcher and head of marine environmental research at Burapha University’s Institute of Marine Science, saying: “What we’re actually seeing with the naked eye is a colour that comes from a type of plankton called Noctiluca,” His team of four was collecting water samples, measuring water quality and taking samples to a laboratory to identify species and build a database. The reports available through October 2 do not provide a final species identification for this event.
A past finding should not be mistaken for a current result. The Thaiger reported that Thailand’s Department of Marine and Coastal Resources identified Noctiluca scintillans during a Koh Larn bloom in 2023; that finding does not establish which species was present in 2026. The Thaiger’s report makes that distinction relevant to the current event.
Rank #2
Does green water mean pollution?
No. Green color alone does not establish sewage contamination or another pollution source. The reports reviewed attribute the discoloration to a suspected plankton bloom, while describing sampling as ongoing; they do not provide final results that confirm either a particular species or a pollution source.
Is the green water safe to swim in?
The available reporting does not establish final water-test results or current official swimming advice for each affected beach, so it cannot settle whether a particular stretch is safe. Reuters reported that some swimmers stayed out of the water and vendors noticed fewer customers; those observations describe visitor behavior, not a measured health risk.
Free tools Windows power users keep installed
One-click scans. No signup required.
Pattaya Mail advises visitors to avoid water with an unusual smell, heavy surface scum or many dead marine animals. That is the outlet’s precaution, not a beach-specific official clearance or warning. Check current local or official guidance before swimming, especially if conditions at the beach have changed.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Could a plankton bloom affect marine life?
Plankton die-off can consume oxygen as it decays, potentially creating hypoxic conditions. Reuters also reported that Burapha University deputy director Anukul Buranapratheprat discussed worsening hypoxia in the inner Gulf of Thailand in broader terms. That background concern does not show that this Koh Larn event had already caused a measured low-oxygen zone.
The reports do not establish how long the discoloration lasted, how large an area it covered, or event-specific water-quality or economic measurements.
Quick Recap
Product prices and availability are accurate as of the date/time indicated and are subject to change. Any price and availability information displayed on Amazon at the time of purchase will apply.
What’s actually slowing this PC down?
Pick the symptom - the matching free tool is one click away.
