PATTAYA, Thailand: Seawater around parts of Koh Larn in Pattaya has taken on an unusual green color, surprising tourists visiting the island, local reports said on September 30th, 2026. Officials, however, said this is normal after heavy rains as recently experienced and nothing unusual.
Authorities and observers said the discoloration is consistent with a naturally occurring plankton bloom, a phenomenon in which microscopic marine organisms multiply rapidly and change the appearance of the water. Such events are more common during the rainy season.
The change followed days of heavy rain, strong winds and unsettled weather across Pattaya and nearby areas. Large volumes of freshwater poured into the sea, carrying nutrients and sediment from land. Those conditions can fuel a sudden increase in plankton, turning seawater green or another color depending on the type and density of the organisms.
The Department of Marine and Coastal Resources said seawater discoloration occurs when plankton populations surge. Nutrient levels near the coast, currents, water temperature and weather all play a role. During the rainy season, runoff from land can deliver extra nutrients into coastal waters.
Officials said plankton blooms often appear after intense rainfall and a large influx of freshwater, and that conditions typically return to normal over time.