HÀ NỘI — The recent mass fish deaths in several lakes in Hà Nội were in part caused by untreated wastewater discharge and weather changes, the city’s People’s Committee has said.

Water in the city’s lakes was contaminated by industrial wastewater, since most of the lakes serve as retention basins. Waste and wastewater discharged by locals also polluted the lakes, the committee announced yesterday .

Change in weather conditions led to a lack of oxygen and reduced the level of dissolved oxygen in water, a factor essential for the respiration of aquatic organisms.

The fact that citizens are allowed to raise fish for business purpose in the lakes also affects the lakes’ water environment, according to the committee.

Over the last months, mass fish deaths occurred in the major lakes of Đống Đa, Linh Đàm, Văn Quán and Ngọc Khánh. 

More than 200 tonnes of fish died in the West Lake at the beginning of October, a mass death for which the city has not provided a specific explanation.

Results from environmental observations conducted by the city’s Centre for Environmental Monitoring Portal in 2011-16 showed that except for iron, all water specifications in all of the city’s lakes exceeded national standards.

The level of mineral oil in water of the 2015-16 period was higher than that of the 2012-13 period and exceeded the national standard several times.

Most of the 117 ponds and lakes in the city are contaminated by wastewater, sediment and sludge, according to the city’s reports.

The amount of wastewater discharged into the lakes exceeded their capacity to filter themselves, polluting them with organic compounds, grease and heavy metals.

Litter that came from several food vendors around the lake also dirtied the surface area, the reports said.

Within this year, the city has directed the Hà Nội Sewerage and Drainage Limited Company to fix the pollution situation of 58 lakes with the German product Redoxy-3C.

Following the city’s directions, the concerned authorities and units will increase inspection of waste treatment by businesses around the lakes, maintain water quality in the lakes that have been cleaned and facilitate the completion of the lake renovation projects.

The city will also employ different communication tools to raise awareness of citizens that live around the lakes on protecting the lakes’ environment and the general environment of the city.  — VNS