Thai beach closed as algal bloom turns waters green, threatens marine life

Beachgoers visiting Ko Lan, a popular tourist destination near Pattaya in Rayong Province, have been warned to stay out of the water as a thick plankton bloom discolours the normally clear seas. The algal growth has transformed the coastal waters into a greenish hue, creating unsightly conditions that have deterred swimmers and raised concerns among marine researchers.

The plankton bloom has been attributed to recent heavy rains and flooding in the region, which have increased nutrient runoff into the sea. These excess nutrients, combined with warm water temperatures, have created ideal conditions for rapid plankton multiplication, a phenomenon that occurs periodically in Southeast Asian waters during the wet season.

Scientists monitoring the situation have expressed concern about the broader implications of the bloom. The rapid growth of plankton consumes oxygen in the water column, creating hypoxic—or oxygen-depleted—zones where marine life cannot survive. Researchers warn that such dead zones are becoming increasingly common and persistent in Thai coastal waters.

Local authorities have advised swimmers to avoid the area until conditions improve. The bloom is expected to dissipate naturally as weather patterns change and nutrient levels stabilise, though no specific timeline has been provided. Environmental officials have called for better management of coastal runoff to prevent future occurrences.