The river is the fresh water source for the Vinaconex Water Supply Joint Stock Company (Viwasupco), which supplies potable water to 250,000 families in 10 districts in southwestern Hanoi.

They are looking to press charges of causing environmental pollution.

On Tuesday last week, a 2.5 ton truck was seen dumping used oil into a mountain creek in Phu Minh Commune, Ky Son District. The oil spread contaminated the Tram Stream and then the Dam Bai Lake, where water is stored to be processed by Viwasupco.

Two days later, Hanoi residents detected an unpleasant, pungent odor in their tap water. Tests of the smelly water by authorities later found that the level of styrene, an organic compound that is probably carcinogenic, was 1.3-3.6 times higher than normal.

Hanoi authorities then warned residents that they should not use the water for drinking or cooking, only for other purposes like washing clothes and bathing. They also demanded that Hoa Binh and local police find the truck and the driver that perpetrated the contamination, but there was no word on the matter till now.

Viwasupco currently supplies 300,000 cubic meters of water per day. Around one million people or one eighth of the capital city's residents depend on its supply.