Hanoi authorities plan to encourage the growth of water plants in the city's lakes to offset chronic pollution.

The biological approach to purifying the capital's lakes has received apositive response from the municipal People's Committee, said ProfessorDuong Duc Tien, director of the Biology Technology for Life Centre.

Tien and his team plan to build organic filter houses on the sides ofthe city's lakes. The proposal will be submitted to city leaders by theend of the year.

Meanwhile, bamboo rafts have beentested on a number of Hanoi 's most polluted lakes, such as ThanhCong, Giam and Thien Quang, as a cost-effective alternative to expensivechemicals.

Mai Dinh Yen, a biology professor atHanoi National University , said official attitudes to lakepollution have changed.

"The acceptance of the idea initself demonstrates local leaders' awareness of the problem and howbest to tackle it. People used to think water plants tarnished theappearance of lakes," Yen said.

Aquatic plants such asreeds, hyacinth, evergreens and lettuce have very large roots, whichcan absorb organic substances and heavy metals dissolved in the water,Tien said.

Yen said the organic approach to tackling water pollution has been used throughout the world since the 1970s.

"That goes for developed countries such as Japan and Germany ," he said.

Dr Tang Thi Chinh, head of the Environment Micro-organism Departmentat the Environment Technology Institute, also supported the use ofaquatic plants to purify the city's lakes.

She saidmost of the lakes in Hanoi and across the country were polluted byan excessive amounts of nitrates and phosphorus, which plants require togrow.

She also said the organic approach is also far cheaper than using expensive chemicals.

"Aquatic plants are in general very cheap. Some of them are wild andvery popular in the countryside where water is polluted," Yen said.

"The Government can only afford to chemically treat two or threelakes. That money could be far more effectively spent on the biologicalmethod," Tien said.

He said it costs 2,500 VND topurify 1 cubic metre of lake water using a chemical formula developed byHanoi scientists. It would therefore cost 250 million VND (12,500USD) to purify a relatively small 100,000 cubic metre lake.

Both Tien and Yen also said that chemical treatment could harm biological ecosystems, as could dredge.

However, experts warn that aquatic plants, such as hyacinth, needed tobe closely monitored so that they didn't overwhelm a lake and cut offsunlight to other water plants.

Yen also said that different plants were better suited to combating certain types of pollution.

"There's an urgent need for more scientific research on this," he said.

They also said that public awareness about the need to keep the city's lakes clean needed to be improved.

"If people throw litter or discharge sewage into lakes, there's no wayto keep the water free of pollution," said Le Ha Vinh, a member of aresidential association in Dong Da district's Nguyen Phuc Lai street,close to Hoang Cau Lake.

Some 95 percent of the 120lakes in central Hanoi are polluted, according to the Centre forEnvironment and Community Research.

Most of the lakeshave a BOD5 (Five-day Biochemical Oxygen Demand) rating higher than the15 milligrams per litre – the maximum considered safe.

Van Chuong, Giam, Linh Quang, Ngoc Khanh and Truc Bach have a BOD5rating of 40-50 miligrammes per litre, due primarily to untreatedsewage./.