The river, which runs through 12 provinces, is the main water supply for more than 10 million people living in the river basin and the people of HCM City.

The contamination has risen to alarming levels after 30 or 40 years’ pollution from many industrial zones along the Dong Nai River basin, according to deputy director of the Dong Nai Centre for Environmental Observations and Engineering, Le Viet Binh.

More than 100 industrial zones in the basin discharge millions of cubic metres of waste-water into the river each day.

During the next 10 years, 100 factories from Bien Hoa 1 Industrial Zone will be relocated, according to the provincial People’s Committee.

The project, to cost VND19.99 trillion (US$809 million), is being undertaken to stop waste water from the factories being discharged into Dong Nai River,

The 320-ha Bien Hoa 1 Industrial Zone, the first industrial zone in the southern part of Viet Nam, was established in 1963.

However, it lacks an effective waste-water treatment system. The existing system is described as outdated.

The zone’s waste-water has, for years, been discharged directly into the river, creating serious pollution.

"It’s time to take action to protect the environment," said chairman of the provincial People’s Committee, Dinh Quoc Thai.

Under the project, more than 100 factories will be moved to Giang Dien Industrial Zone in Trang Bom District, and other industrial zones in the province, including Nhon Trach No 1, 2, 3, 4 and Ong Keo.

The relocation will start later this year and will be completed by 2022 as the urban trade and services zone is established.

The project has met with approval from most of the enterprises, said Thai. The province will provide the transferred industries with compensation, support and a high level of incentives to make the move.

According to Do Thi Thu Hang, chairwoman of the board of the Management Development Corporation for the Bien Hoa Industrial Zone (Sonadezi), this will amount to about VND3.7 trillion ($176 million) in total.

The Department of Natural Resources and Environment said the present amount of waste-water pumped into the river amounted to about 8,600 cubic metre per day.

After many fines for polluting the environment and related violations, industrialists claim that 95 per cent of waste-water is treated before being released.

However, an analysis of water samples taken from the Dong Nai River has revealed contamination still exceeds permitted levels.

This has largely been blamed on effluent from 10 factories in the zone, said the Ministry of Natural Resources and Environment.