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Prolonged rain, waste caused mass fish death in La Nga river

Changes to the water environment on the La Nga river in the southern province of Dong Nai have been blamed for the death of nearly 1,000 tonnes of fish this month, provincial officials have said.

Vice Chairman of the Dong Nai Province People’s Committee Vo Van Chanh said that as soon as the mass fish death on the river in the province’s La Nga and Phu Ngoc communes was reported, the Southern Environment Observation Centre, Zone VI Animal Health Department and the provincial Department of Natural Resources and Environment took water samples.

Test results showed the concentrations of ammonia, nitrite and the chemical oxygen demand (COD) in samples were in excess of levels allowed in aquaculture farming, Chanh said.

Director of the provincial Department of Agriculture and Rural Development Huynh Thanh Vinh said rain lasting from May 15 to early morning of May 16 made waste flow into the river, lowering the dissolved oxygen content in the river’s surface water, killing the fish.

The concentration of ammonia in water river samples was 4-7 times higher than permitted, the nitrite concentration 2-3 times higher than permitted and the COD concentration 3-16 times higher than permitted.

Moreover, testers found no signs of common diseases or infectious diseases that freshwater fish tend to contract.

According to the department, last June, more than 1,900 tonnes of fish from 132 local households were found dead along the 5km La Nga river after heavy downpours.

The low oxygen level in the water and the high density of fish were reported as the main cause of the mass deaths at that time. Pollution from upstream areas swept down by the rains worsened the incident.

As of last December, the provincial People’s Committee had spent more than 12 billion VND (516,000 USD) to support affected households in Phu Ngoc and La Nga communes.

Vinh said the department planned to help fish farming households who were affected by the recent mass fish death.

Deputy Prime Minister Truong Hoa Binh on May 28 asked for further investigation into the cause of the mass fish death and hand out appropriate punishments to those who violated the laws.

Binh also ordered Dong Nai authorities to review the major sources of waste discharged into the La Nga river, particularly giving focus to the cases that received complaints from the public.

A thorough report is expected to be submitted to the Prime Minister before June 30.