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Plankton bloom turns Thai island waters a bright, smelly green
Researchers said heavy rains and floods fed the bloom, while some beach vendors reported fewer customers as swimmers stayed out of the water.
On Thursday, Oct 1, 2026, the sea off the tourist island of Koh Lan in Thailand turned a bright, pungent green due to a plankton bloom, forcing swimmers to avoid affected coastal areas.
Significant flooding in Thailand in recent weeks, combined with fertiliser runoff and warmer seas linked to climate change, has increased freshwater volume and fueled rapid plankton growth in the Gulf.
Arvut Munhapon, a senior researcher at the Marine Science Research Division, identified the organism as Noctiluca. Tourists like 29-year-old Latipeya Thantibhapat avoided the water, fearing skin rashes.
Mass plankton die-offs create hypoxic "aquatic dead zone" conditions, according to Anukul Buranapratheprat of the Marine Science Research Division. Food vendors reported fewer customers as visitors avoided the discoloured water.
While blooms typically last two to three days, researchers warn that this year's monsoons may intensify both the bloom and hypoxic conditions in the Gulf.