Their hope stems from the quality improvements seen a week after a nano-biotech treatment was applied, beginning May 16.

Specifically, the amount of ammonia in the river, which made it stink, reduced drastically three days after the Nano-Bioreactor technology was used, said Nguyen Tuan Anh, chairman of the Japan-Vietnam Environmental Improvement Company (JVE) which is carrying out the pilot project.

He said Friday that the sludge at the bottom of the river had also partly decomposed a week after, producing a layer of clear water above it.

"These results are announced only for experts to know of changes to the initial metrics, so we are not going into details. Scientifically speaking, water quality metrics can only be accurately measured after a month or two [of applying the technology].

"After two months, the amount of sludge in the river would be drastically reduced and the water would be clear again. We can even raise fish in the river then," said Anh.

In some river sections affected by the biotechnology, the water has changed from pitch black to milky white.

"My family used to close our doors and windows all the time because we could not stand the stench [coming from the river]. Ever since the technology’s been used, the stench has reduced drastically. We can even go outside in the afternoon for a walk," said 60-year-old Nguyen Van Thang, who lives near the river sections being treated with the new technology.

The Nano-Bioreactor technology, provided by Japanese experts, produces oxygen in the water by activating both aerobic and anaerobic microorganisms in the water. Equipment use includes an aerator to quickly treat water using natural materials, which is installed on the bed of the river.

The water quality results are expected to be released by the end of this month.

In October 2016, Hanoi started work on a $726 million sewage treatment plant which was expected to be completed in three years. The plant will be able to treat 270,000 cubic meters of sewage collected from the Lu, To Lich and Nhue rivers every day.

Hanoi’s To Lich River, which runs from the Cau Giay District to the Nhue River in Thanh Tri District, is 14 kilometers long. An estimated 150,000 cubic meters of unprocessed sewage is released into the river every day, according to the Hanoi Department of Natural Resources and Environment.