PATTAYA, Thailand – Tourists visiting Koh Larn were surprised on September 30 when sections of the sea around the popular island turned noticeably green, prompting questions about whether the unusual color was linked to pollution.
Pattaya authorities said the change in color is believed to be associated with a natural phenomenon known as a plankton bloom, in which marine plankton multiply rapidly and can change the color of seawater. The explanation is consistent with conditions around Pattaya in recent days, which have included heavy rain, strong winds and unsettled weather.
Heavy rainfall can send increased amounts of freshwater, sediment and nutrients from the mainland into coastal waters. The additional nutrients can provide conditions for plankton to multiply, particularly during the rainy season. Thailand’s Department of Marine and Coastal Resources also identifies nutrients washed from land during the rainy season as an important factor behind seawater color changes.
Reports from Koh Larn indicate that the green color has been particularly noticeable around Tawaen Beach, while the phenomenon does not necessarily affect every beach around the island. Similar green-water events have been observed around Koh Larn during rainy periods in previous years.
The color change is expected to be temporary and can gradually disappear when the weather, water movement and other conditions supporting the plankton bloom return to normal. Local reports have suggested the water could clear within several days, although the timing can vary.
For visitors, the green colour alone should not automatically be taken as evidence of sewage or other pollution. However, if seawater develops an unusual smell, heavy surface scum or is accompanied by significant numbers of dead marine animals, visitors should avoid entering the water and follow advice from marine and environmental authorities.
Pattaya City said it will continue monitoring the situation while Koh Larn remains open to visitors. The island continues to welcome tourists, with conditions varying between beaches as the natural phenomenon develops and fades.
