It plans to build a sewer system of 13 kilometers (7.5 miles) under the river bed to collect and send wastewater to a treatment plant in Yen Xa in Thanh Tri District.

Authorities would hear various agencies present methods and specific steps to carry out the project at a meeting on Friday, city Chairman Nguyen Duc Chung said on Tuesday while inspecting the construction of the Yen Xa plant.

The plant will have a facility to treat 270,000 cubic meters of wastewater a day and a system to collect wastewater that will be connected with To Lich and Lu rivers and Ha Dong District.

Sewers will run more than 52 km in total, including 21 km to collect from the To Lich, including almost 13 km under its bed.

A Japanese contractor has already won the bid to build the sewer system, and the work is expected to begin this quarter and be completed in 48 months.

Chung said the construction of sewers under the riverbed is convenient since it would speed up the entire project, be cheaper and not affect traffic.

"Once the Yen Xa project is completed, all wastewater discharged directly into the To Lich will be treated 100 percent."

Plans to renovate the areas around the river have also been drafted.

The Department of Construction will improve a 16-km section along both banks of the river by growing trees and creating spaces for pedestrian streets while the Department of Transport will build three walking bridges across the river.

The renovation is scheduled to be finished before the sewer system and wastewater treatment plant are ready.

To Lich River used to be a branch of 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 black water.

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

Some plans were not implemented and some that were tried out did not work.

The Japan-Vietnam Environmental Improvement Company tried last year to clean a part of the river by installing nanotechnology equipment on a 300-meter section.

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

The Japanese team working on it ended its pilot project in November without announcing if the work was a success or not.

Hanoi later said the project did not work.