The river supplies water for about 12 million people and about 1.8 million hectares of cultivated land around HCM City and 11 surrounding provinces.

The river is polluted by untreated waste water from millions of households and thousands of factories. Hydroelectricity generation, irrigation and other activities have also contributed to the pollution.

In downstream areas below the Tri An Hydro-power Reservoir and Dau Tieng Reservoir to the river's mouth, water is heavily polluted in many areas, according to southern Dong Nai Province's Environmental Observation Centre.

While water quality has declined, water shortages have occurred during the dry season, making residents in four districts in Dong Nai Province struggle hard to find water for daily use and production.

Le Viet Hung, director of the province's Department of Natural Resources and Environment, said the Dong Nai River's Section 3 exceeded permissible levels for the quantity of pollutants, including organic substances, iron and bacteria.

Lam Thi Thu Suu, a coordinator of the Vietnam Rivers Network, said Dong Nai River in particular, as well as many other rivers in the country, had been over-exploited for hydro-power plant operations.

Discharged pollutants in downstream areas have also caused severe pollution in the river.

Experts have urged each province to collect and treat waste water before releasing it into the river.

They said that a project to protect the Dong Nai River basin, approved by the Government in 2007, needed to be implemented as soon as possible.

The project, to run until 2020 at a cost of VND2 trillion (US$95 million), targets solving pollution problems at 90 per cent of factories located along the river by 2015.

It also aims to have waste water treatment systems at all industrial parks, export processing zones and hi-tech industrial zones along the river by 2020.

Experts said provinces should also develop measures to control illegal deforestation and protect the river's ecological system.

Factories, industrial parks and hydro-power plants should no longer be built in the river's upstream areas, they said.