“All the fish in the Song May reservoir died for lack of water,” a local resident in Trang Bom district, who identified himself only as Nghia, told AFP.
“Our life has been turned upside down over the past 10 days because of the smell.”
Pictures show residents wading and boating through the 300ha Song May reservoir, with the water barely visible under a blanket of dead marine life.
According to media reports, the area has seen no rain for weeks and the water in the reservoir is too low for the creatures to survive.
Reservoir management had previously discharged water to try to save crops downstream, Nghia said.
“They then tried to renovate the reservoir, bringing in a pump to take the mud out so that the fish would have more space and water,” he said.
However, the efforts did not work and, shortly afterwards, many of the fish died, with local media reports suggesting as many as two hundred tonnes’ worth of fish may have perished.