The HCM City authority has sent a proposal to Prime Minister Nguyen Tan Dung requesting the Government to suspend construction of 20 hydro-power projects along Dong Nai River.

Construction of more than 20 hydro-power projects on the upper section of Dong Nai River, without a comprehensive study of their impact, could seriously affect environmental conditions of provinces in the lower section of the river, including Binh Duong, Dong Nai and Ba Ria-Vung Tau as well as HCM City, said Nguyen Van Lai, director of the city's Department of Industry and Trade.

Lai said HCM City should heed the warnings about such impact, since the water released from reservoirs in central provinces had caused flooding, evidence of the severe environmental impact of the numerous hydropower plants that had been built without any master plan.

He said construction of a hydro-power plant reservoir required destruction of a vast area of forest. The reduction of natural forests would lead to a lower underground water level and exhaustion of water resources.

Nguyen Van Nga, head of the city's Department of Natural Resources and Environment's Water Resources Management Division, said water quality and quantity in Dong Nai River had deteriorated since 2009.

The intrusion of salt water into untreated water pumping stations of the Sai Gon Water Supply Co on Dong Nai River is threatening the city's water supply, said Nga.

Due to the salt water intrusion, the Tan Hiep and Thu Duc pumping stations have had to suspend pumping untreated water two to six hours per day, affecting water supply resources for HCM City.

Nga added that during the last dry season, the water level in Dong Nai River was 20cm lower and salt water intrusion had been reported two months earlier than in previous years.

Prof Doan Canh of the Tropical Engineering Institute said the existing hydro-power plants on Dong Nai River had seriously affected the water level of the river.

Apart from the reduction of underground water reserves, the strong stream flows from hydro-power plants had been destroying the ecological systems along the banks of Dong Nai River.

These stream flows had not only caused water erosion on both banks of the river but had also contributed to flooding in the lower section of the river.

Meanwhile, an official from the Ministry of Industry and Trade said it was difficult to control the construction of all small-scale hydro-power plants.

Unplanned development of medium – and small-sized hydro-power plants was a chief cause of more serious flooding that had occurred recently in Vietnam's central provinces./.