The incident occurred at the CV1 Lake on May 29 and 30, with large numbers of dead fish floating on the water and accumulating along the lake's concrete embankments.
In several areas, fish carcasses formed dense clusters on the surface, while household waste, including foam containers, plastic bottles and plastic bags, was also seen floating in the water.
Nearly 60 workers from Hanoi Drainage Company No. 2 were deployed to collect the dead fish and floating waste before transporting them to Nam Son waste treatment facility.
By the end of May 30, most of the dead fish had been cleared from the lake.
A representative of the company said the fish deaths were likely caused by a sudden change in water temperature after a prolonged period of extreme heat was followed by heavy rainfall.
More than 10 tonnes of dead fish were collected during the clean-up operation, according to the company.
The CV1 park and lakel complex covers about 27 hectares and was put into operation in the second quarter of 2024 following an investment of VND 744 billion.