Black seawater along the coast of Quang Ngai.
Photo by VnExpress/Pham Linh. 

Seawater near ports of the Dung Quat Economic Zone in the central province of Quang Ngai has turned dark black for the last 10 days. 

The color change can be seen on a length of nearly 200 meters on the coast.

Nguyen Duy Khac, a commune chairman in the area, also said that when the waves retreat, a black viscous residue can be seen on the sand.

Black and viscous residue left on the sand when the waves recede.
Photo by VnExpress/Pham Linh.

The water is part of a tourist area and has always been clean blue, according to locals.

They suspect that the cause of this severe contamination is untreated sewage discharge from heavy industry factories at the Dung Quat Economic Zone.

Environment officials have taken samples of the contaminated seawater for examination.