Monday’s rain washed polluted water into a major canal in Ho Chi Minh City, having killed 70 metric tons of fish there so far, local authorities said on Wednesday.

The 8.7-km Nhieu Loc–Thi Nghe canal was filled with the floating bodies of dead fish on Tuesday morning, following rainfall in several parts of the southern metropolis on Monday afternoon.

The city’s Party Committee had tasked relevant agencies with determining the cause of the death, and held a press conference yesterday to announce their results.

The municipal environmental department said that as of 5:00 pm on Tuesday, 14 metric tons of dead fish had been retrieved for destruction, with 16 canoes and dozens of employees sent to the canal to retrieve the deceased fish.

That number rose to 70 metric tons at noon on Wednesday.

Nguyen Phuoc Trung, director of the agriculture department, said his officials had taken samples of the canal water right after the rain on Monday for testing.

“The initial cause of the fish death is pollutants and toxic gas washed into the canal by the rain,” Trung said.

Test results found that the canal water had multiple parameters exceed allowable levels, including water transparency, pH levels, and ammonium and ammonia contents, according to Trung.

He said the latest fish death is not unprecedented, as similar incidents were recorded in May 2014 and 2015, when Ho Chi Minh City began its rainy season.

“The latest test results are similar to those taken in the two previous years,” he said.

The Nhieu Loc–Thi Nghe canal snakes through District 1, District 3, Phu Nhuan District, Binh Thanh District and Tan Binh District. Once heavily polluted and dubbed a ‘dead canal’ back in the 1950s, it was revitalized following an expensive clean-up project, the first phase of which ended in 2012.

Other major canals in Ho Chi Minh City include Tau Hu–Ben Nghe and Tan Hoa–Lo Gom.

Tran Van Son, deputy head of the agency in charge of inspecting water quality in Ho Chi Minh City, said Nhieu Loc–Thi Nghe was the only canal that suffered, as it is linked to a sewage system where wastewater from many areas of Tan Binh District is discharged to.

“The water [on Nhieu Loc–Thi Nghe] is almost not flowing, whereas other canals such as Tau Hu–Ben Nghe are linked with nearby waterways and connected with the Saigon River,” he elaborated.

Besides the dirty water washed up with the rain, Nhieu Loc–Thi Nghe also suffers because of the amount of garbage dumped directly into the canal by households on both its sides.

The city’s agriculture department has so far sprayed five metric tons of zeolite, a common chemical used in water treatment, into the canal to disinfect the polluted water.

“In the longer term, we need a comprehensive solution, such as treating the sewage water before it is dumped into the canal,” Trung, the department director, pressed.