The plan is to direct water from the Red River, which flows from Yunnan Province in Southwest China through northern Vietnam to the Gulf of Tonkin, to the West Lake via a penstock system for processing.

Then, from the West Lake, the biggest freshwater lake in the capital city, water will be directed to To Lich, which has been heavily polluted for years.

The entire system to lead the water from the Red River to the West Lake is expected to be around two kilometers long.

After the water arrives at a filter next to the lake for all sediment to be left behind, it will be pumped into the lake, and when the water in the lake reaches a certain level, the Hanoi Sewerage and Drainage Company will open floodgates to send it to the To Lich River.

Under the plan, over 134,000 cubic meters of water from the Red River would be directed to the West Lake every day. The project is expected to cost VND150 billion ($6.5 million).

It's not clear when and for how long the project will be conducted.

The To Lich River used to be a branch of the Red River but was delinked by the French in 1889 as part of an urbanization plan.

Over 200 sewage outlets empty 150,000 cubic meters of untreated household wastewater every day into it, according to the city Department of Natural Resources and Environment. Wastewater from factories adds to the pollution.

The river runs 14 kilometers (8.7 miles) through the downtown districts of Thanh Xuan, Hoang Mai and Thanh Tri and has become infamous for its stench and blackish water.

Hanoi has tried in vain to clean To Lich many times in the last decade.

The West Lake, however, has also been suffering from pollution and sometimes, a serious lack of water.

The new plan to clean up the To Lich River with water from the Red River had been suggested by Russian experts in 1981, said To Anh Tuan, deputy director of Hanoi’s Department of Planning and Architecture. However, it was not implemented as other ideas had come up to deal with pollution of the To Lich River.

For different reasons, some ideas were not implemented and some that were tried out did not work.

Most recently, the Japan-Vietnam Environmental Improvement Company started a project in May to clean a part of To Lich by installing nanotechnology equipment on a 300-meter section of the river.

The equipment was provided by the Japan's Trade-Environment Promotion Organization. The nano-bioreactor technology would infuse oxygen into the river to activate beneficial microorganisms and create an environment for them to live in.

Last Sunday, the Japanese team ended their pilot project without announcing whethere it was a success or not.

Tuan said the Red River project would have to show that it can create more economic, social and environmental benefits than previous ones.

"It also needs to map out a plan to improve the environment around the To Lich River and the West Lake once they have been cleaned up, to add cultural and scenic values for the city," he said.

Le Minh Chau, former director of Hanoi Sewerage and Drainage Company, cleaning up the environment of the To Lich River and the West Lake had become an urgent task.

"If the current pollution continues unchecked, West Lake will become a pond and To Lich would be a dead river," he said.

Dong Minh Son, former deputy chairman of Hanoi, said residents on the city outskirts have been saying for years that water from the To Lich River and several other branches of the Red River from the inner-city was so polluted they could not be used for watering plants even.

He said pumping water from the Red River to the To Lich River in an attempt to wash away pollution was a necessary initative, but for long term, the city needs more comprehensive solutions to deal with the environment of its rivers and lakes.