Southern Dong Nai Province’s agriculture department said the unsual high level of NH4 (Amoni) and NO2 (Nitrite) may be the reason behind Monday’s mass fish deaths on the La Nga River based on a test done on water sample collected at the site.

Mass fish deaths on the La Nga River.

The test showed a NH4 level 5.6-11 times higher than farm fish tolerance level while NO2 was found to be at 10-20 times higher. In addition, dissolved oxygen level on surface water was at 2.6-3.2mg/l, significantly lower than the recommended level of 4.0mg/l.

The department said there was a heavy rainfall, which lasted well over seven hours prior to the incident. It was possible that a large volume of water heading from upstream carried enough pollution, which in combination with NH4 and NO2 was deadly to the fish.

“Exactly how it happened will be revealed after more tests are done on water and fish samples,” said Huynh Thanh Vinh, the provincial agriculture department’s director.

Vinh also said if natural causes were the cause of mass fish deaths, around 80 fish farming households would eligible for support from the Government. At the estimated 1,500 tonnes of fish loss, they can be compensated up to US$400.000.

The authority hasn’t ruled out man-made causes such as toxic water discharged by factories upstream. The case is still under investigation. — VNS