A seasonal natural event known as a plankton bloom is currently visible along Hua Hin Beach, turning the sea green during the day and creating bioluminescent blue waves after dark.
The phenomenon, which typically occurs once a year, is caused by a surge in phytoplankton — microscopic marine organisms that multiply rapidly under certain environmental conditions. Their natural pigments are responsible for the change in the water’s appearance.
The bloom was first spotted earlier this week off Cha-am beach and has since been seen near the Tubtim shrine in Hua Hin. According to experts, the discolouration is not harmful, and swimming in the sea remains safe.
The plankton bloom often occurs during the summer months, particularly from March to May, although instances have also been recorded in January. The event typically lasts for several days, with conditions expected to return to normal within a week.
While the bloom itself poses no health risks, it may sometimes cause unpleasant odours in isolated spots. Individuals with sensitive skin are advised to take precautions, though no formal warnings have been issued.
The greenish tint seen during the day is due to the high concentration of plankton, which can also lead to reduced oxygen levels in the water. However, marine specialists note that these changes are temporary and part of a recurring cycle influenced by sea temperature, wind patterns, and nutrient levels.
At night, the phenomenon takes on a different form. The same plankton responsible for the green hue produce a glowing blue light when disturbed by waves, swimmers, or passing boats. This effect, known as bioluminescence, is caused by a chemical reaction within the plankton, primarily dinoflagellates, and is thought to serve as a defence mechanism.
The intensity of the glow depends on several environmental factors, including water movement, temperature, and nutrient availability.
Tourists and residents have been gathering at the beach after sunset to witness the glowing waves, which offer a rare and striking visual experience.
