Fish have been seen dying en mass in Hoang Cau Lake in Hanoi since June 8 morning.
Local people said they found some dead fish floating on the water while doing morning exercises near the lake on June 8. By late afternoon, lots of fish have died.
Mr.Tam, who raises fish in the lake said that he was going to harvest more than 100 tonnes of fish from the lake but now almost half of them have died.
Local people said that the fish died following a heavy rainfall on Tuesday afternoon and early Wednesday morning when sewage run into the lake along with rainwater.
Environment workers and local people have come to collect the dead fish but some parts of the lake still had a rotten smell