Lakes such as Ngoc Khanh, Kim Lien, Ba Mau and Thien Quang were once severely contaminated and needed urgent cleaning to protect their bio-systems, safety levels and the surrounding areas.
"I’ve seen a big improvement. The water in the lake [Ngoc Khanh Lake] is cleaner and less smelly," said Vu Khac Hoa, a resident of Hanoi’s Ba Dinh district, who lives near Ngoc Khanh Lake.
The surrounding area had also been beautified, he said.
“The investor has separated the water drainage system so the waste water from residential areas no longer flows into the lake,” Van Dinh Hung, another resident told Vietnam Television.
Bui Ngoc Uyen, from the Hanoi Sewage and Drainage Company, which is responsible for maintaining Hanoi’s lakes, said over the past year the company has used chemical products together with a number of measures like the installation of aquatic rafts with a view to increase oxygen and the self-cleaning ability of the lakes.
The main task for Hanoi lakes is to regulate drainage, drought and environmental landscapes and they have met these criteria, experts say.
According to the Centre for Environment and Community Research (CECR) report released in 2015, the number of lakes in Hanoi decreased to 112 from 122 between 2010 and 2015. The water surface also dropped by72,000sq.m compared to 2010.
Data from the CECR analysis showed that a lot of lakes, which were once beautiful spots for the city’s residents to visit and enjoy, were seriously deteriorating due to rising levels of pollution.
Test on water samples taken at these lakes revealed that lakes contained an excessive amount of pollution, compared to national standards.
To improve the water environment at lakes, the municipal People’s Committee had assigned the Department of Natural Resources and Environment to research and implement the testing and treatment of water pollution in rivers and lakes in the city.
The experiment was conducted in 12 lakes including Ngoc Khanh, Xa Dan, Hai Ba Trung, Kim Lien, Ngoc Ha, Den Lu, Van Quan and Giang Vo. In addition, the Department handled the pollution of water in Ho Tay (near the Water Park) and My Dinh ditch.
In 2016, the municipal People’s Committee has directed the Hanoi Sewage and Drainage Company to implement the treatment of Redoxy-3C technology for 83 lakes in the city to enhance the water quality.
After the product was proved effective during trials in Ho Me, Ba Mau and Giap Bat Lakes, Redoxy-3C has been applied to other lakes in the city including Hoan Kiem Lake (Sword Lake).
Covering an area of around 12 hectares, the lake is located in the historical centre of the city. Not only important historically, Hoan Kiem Lake has a beautiful landscape, and is considered a scenic, relaxing escape from the chaos of the Old Quarter.
However, the lake is severely polluted and has lost the ability to revive itself. Its water quality is getting worse by the day, its pH level is high, and the amount of suspended deposits is higher than the permissible limit at all five monitoring locations, according to the Hanoi Sewage and Drainage Company.
The lake also has high organic contamination, with the indices for both biochemical oxygen demand (BOD) and chemical oxygen demand (COD) two times over the limit.
The lake water has lost its distinctive dark green colour in several spots, and there is a one-metre layer of mud at the bottom of the lake, causing pollution and reducing the water level by 0.5 to 0.8m.
By the end of last year, the company was assigned to dredge and clean Hoan Kiem Lake.
After over one month of cleaning, the original colour of water in the lake has returned and there is no longer a bad smell.
Pham Tung Lam, head of the Management Board of Hoan Kiem Lake, said the polluted mud layer disappeared when the dredging process had finished.
“It would be a good opportunity for creatures to develop in the lake,” he said adding that as a matter of fact, a tortoise had been seen laying eggs near Ngoc Son temple.