Workers collect the oil on Linh Dam Lake on October 1.
According to the Hanoi Drainage Company, the black oil slick was spotted on the lake on the morning of September 27. The company sent workers to collect the oil but the work has not been completed yet.
On the morning of October 2, dead fish started to float around the oil spill.
While local authorities are still investigating the incident, some people said that the oil might have come from wastewater from nearby production facilities.
Tran Thi Minh Hien from the Hanoi Drainage Company said that Hoang Mai District Police Department has come to collect the oil samples for investigation and try to find out where it came from.
"We're co-operating with the police on the investigation while continuing to collect the oil from the lake to deal with the pollution," Hien said.
