Why did Koh Larn’s sea turn green? What visitors should know

What has changed

Parts of the sea around Koh Larn changed colour this week, attracting attention from visitors to the island off Pattaya. Local reporting identified Tawaen Beach among the affected areas on 30 September.

What caused the green water?

Reporting by Thaiger linked the discolouration to a plankton bloom following heavy rain. Runoff can carry nutrients into coastal waters, encouraging rapid plankton growth. The appearance of the water can vary between beaches.

Reuters subsequently reported that Burapha University researchers were sampling the water and investigating the bloom. Its coverage described green patches along parts of the coast, with other stretches unaffected.

Has the water cleared?

Pattaya Mail reported clearer, blue water on 2 October and said ferry and speedboat services were operating.

That update describes an improvement after the earlier discolouration. It should not be treated as a water-quality assessment for every beach or a guarantee of conditions when you arrive.

What should visitors check?

Before a day trip, check the latest local updates and ask your boat operator or accommodation about conditions at the beach you intend to visit. Follow any posted notices and instructions from local officials.

Images taken during the bloom may show conditions that have since changed. Check the date and location before using a photograph or social media post to plan your visit.

This article summarises reporting available on 2 October 2026. Conditions may change, and it will be updated when further verified information becomes available.