Fish raised in a southern Vietnamese river have unexpectedly died in enormous numbers overnight, wreaking havoc on the business of local farmers.

Thousands of tonnes of fish farmed in cages by scores of families died along a two-kilometer-long portion of the La Nga River in Dong Nai Province.

Nguyen Van Nghia, a local farmer, said the incident occurred two times, the first starting at around 9:00 pm on Sunday, with the peak reaching at midnight.

The other commenced at about 2:00 am the following day and continued well until the morning, Nghia said.

From early Monday to the afternoon, multiple trucks parked bumper to bumper on the riverbank while the dead fish were being briskly carried onto them from farming cages.

Residents arrived for some purchases, forming a makeshift marketplace.

People purchase fish along the La Nga River in Dong Nai Province, Vietnam, May 21, 2018. Photo: Tuoi Tre

Dead fish lie on the bank of the La Nga River in Dong Nai Province, Vietnam, May 21, 2018. Photo: Tuoi Tre

Some said they intended to use the dead fish as an organic fertilizer while several others would eat them in their meal.

A trader here told Tuoi Tre (Youth) newspaper that the fish were bought for the production of animal feed, not for human consumption.

The fish, including common carps, red tilapia and catfish, fetched a low price, forcing farmers to incur significant losses.

A leader from the Dong Nai Department of Natural Resources and Environment said the massive deaths must have been caused by a mixture of muddy runoff from a torrential rain on Sunday evening and alluvial materials flowing downstream.

The provincial authorities have taken samples of water in the La Nga River for further examination. They are investigating whether waste from factories along the river is partly to blame.

Men carry fish from a boat along the La Nga River in Dong Nai Province, Vietnam, May 21, 2018. Photo: Tuoi Tre

A man shoulders a basket of fish along the La Nga River in Dong Nai Province, Vietnam, May 21, 2018. Photo: Tuoi Tre

Local fish farmers said that fish deaths have occurred frequently over the past ten years, with the toll ranging from dozens to thousands of tonnes each.

They were told by the authorities that the causes varied from lack of oxygen in water due to pollution from cane molasses flowing from a company’s ruptured molasses tank; a dense population of raised fish; and weather fickleness.

In 2016, two fish death instances were reported at the section of the river of the above case and inflicted significant losses on farmers.

A common carp is weighed in Dong Nai Province, Vietnam, May 21, 2018. Photo: Tuoi Tre

A woman puts a fish into a basket on a boat along the La Nga River in Dong Nai Province, Vietnam, May 21, 2018. Photo: Tuoi Tre

Sacks of dead fish are loaded onto boats along the La Nga River in Dong Nai Province, Vietnam, May 21, 2018. Photo: Tuoi Tre

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