A large area of algal bloom was sighted at Leam Mae Phim Beach, Klaeng, Rayong.
Three kilometres of seawater with an unusual colour and a strong odour was spotted at Leam Mae Phim Beach. No sea creatures were found dead as of Monday.
According to local residents, the seawater started turning green on Oct 1.
The Nirat Muang Klaeng Facebook fan page reported this phenomenon to Suthep Jualaong, the director of the Marine and Coastal Resources Research Centre (Eastern Gulf of Thailand) on Sunday.
After hearing about the concern, the Department of Marine and Coastal Resources immediately ordered the Marine and Coastal Resources Research Centre to conduct an investigation on Monday.
An investigation shows that the seawater quality, measured from a sample collected from the beach, is still safe by measurable and legal standards.
The research centre said the water colour change could be caused by Noctiluca Scintillans, a plankton found in an annual bloom along the eastern seaboard.
This plankton causes a change in seawater colour and a strong odour.
However, it does not produce any biotoxins in the water, which leads to a safe level of water quality.
Atthapon Charoenchansa, the department chief, expressed concern about the phenomenon, as plankton absorbs nutrients like phosphorus and nitrogen from wastewater discharged from industrial sites and residences, resulting in plankton blooms in the sea.
Mr Atthapon revealed that after finding out about this situation, Varawut Silpa-archa, Minister of Natural Resources and Environment, ordered the DMCR and related sectors to investigate and research this phenomenon.
Local people then need to be informed of this type of occurrence, he said.
"The marine and coastal environment are considered precious resources. Every resident is responsible for marine and coastal conservation," said Mr Atthapon.