The black seawater spotted at Patong beach is caused by plankton bloom, which is an annual phenomenon, said a senior official.
The photos of brown and black seawater, seen flowing from Pakbang canal to Patong beach were shared online. The unusual color of the seawater there keeps tourists away from swimming in the sea as they do not know what causes the change in its color.
After inspection at the site, Sitthipol Muangsong, official from Phuket Fisheries Office said that an increase of the large amount of algae made the seawater turn into brown, red, green or black colour.
It happens in summer, depending on tide and wind and lasts for a short period.
The Marine and Coastal Resources research center will collect samples of the seawater for quality testing to create confidence among tourists and locals, he said. (TNA)