Many farmers in central Vietnam have been stunned to find that the fish they raised in a river have died off over the last two days in a case where a local hydroelectric dam might have played a large role.

The incident occurred to hundreds of cages for cultivating various fish along the Bo River in three districts of Thua Thien-Hue Province, causing damage worth of hundreds of millions of dong (over US$9,000).

In a single village in Quang Dien District, 90 out of 169 such cages were discovered to have over 36 tonnes of dead fish, according to Nguyen Trung Tinh, the village’s head.

Nguyen Huu Hoang, a resident in this area, said the river has maintained standing water during the past one month, and he now incurs a loss of VND50 million ($2,150) as more than one metric ton of his adult grass carp has died.

A farmer swims in a fish cultivating cage along the Bo River in Thua Thien-Hue Province, Vietnam, July 10, 2018. Photo: Tuoi Tre

Local farmers said fish in several cages began rising to the water surface with their mouth open in a moribund state at around 8:00 pm on Monday before dying.

The toll reached its climax the following morning.

Most of the fish were grass carp ready to be harvested that weighed between five and seven kilograms.

Some farmers desperately used devices for oxygenating the water in an attempt to keep the other fish alive.

Village leader Tinh attributed the massive deaths to the deprivation of oxygen in the river’s usually stagnant waters, which has been linked to a nearby hydroelectric dam.

“If the hydroelectric plant had discharged water last night [July 9], fish wouldn’t die in large numbers now. We reported the problem with fish yesterday afternoon but only until 10:00 am today did the dam begin releasing water. But most of them had already died by then,” Tinh said.

Large-scale fish deaths happen yearly around July, when the dam reduces its water discharge from a reservoir due to modest rainfall and scorching weather, he added.

A dead fish is weighed on a scale in Thua Thien-Hue Province, Vietnam, July 10, 2018. Photo: Tuoi Tre

Fish-farming cages are seen in the Bo River in Thua Thien-Hue Province, Vietnam, July 10, 2018. Photo: Tuoi Tre

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