At least 23 tons of assorted fish were found dead in Dong Nai River in the province of the same name from Sunday to Tuesday, and industrial sewage could be the culprit, authorities have said.
Fish raised in cages under rafts on the river have continued to die, the provincial Department of Natural Resources and Environment said Tuesday.
The department's inspectors said they identified two sections of the river that showed signs of pollution from two sources, the Tan Mai Paper Company and the Bien Hoa Industrial Park, that both pump wastewater into the river.
The water in the two sections is yellow and has a foul smell, according to the inspectors.
Vu Thi Lieu, a farmer in Bien Hoa Town's Hiep Hoa Commune, said "I have raised fish on the river for eight years, but I have never seen such a large amount of dead fish."
She said at least 1.5 tons of her fish died.
"It is certain that some factory dumped untreated wastewater into the river. If the authorities don't step in, fish farmers will continue to lose out," Tran Duc Can, a farmer in Bien Hoa's Thong Nhat Ward said, adding that 4.5 tons of his fish have perished.
In early May, Quang Ngai Sugar Joint Stock Company's brewery discharged untreated draff wastewater into the Tra Khuc River in the central province of Quang Ngai, killing two tons of marine creatures like fish and crabs.
Some 3,000 ducks in Tinh Khe Commune then died because they ate the contaminated fish and drank water from the river.
Quang Ngai police are looking into the case after the provincial environment and animal health departments concluded that draff wastewater from Quang Ngai Sugar was responsible for the death of fish and ducks.