An environmental worker collects the dead fish in Hoang Cau Lake on May 10
A local resident, Do Van Thanh, said that the fish started to die in the afternoon of May 9.
"We could see many dead fish floating on the lake by the morning of May 10," Thanh said. "The incident often occurs at this time of the year when it changes from spring to summer. Tonnes of fish also died in the lake at this time last year. "
A representative from the Hanoi Water Drainage Company said that they had sent a team to study the cause of the mass fish deaths in Hoang Cau Lake.
"It is estimated that about one tonne of fish died this time," he said. "Initial investigations showed that the fish might have died from the changing weather. The prolonged heat and sudden rain both led to decreased oxygen volume in the lake which might cause the mass fish deaths."
When it rained, wastewater in the area also flowed to the lake, causing pollution which killed the fish, he added.
