Of a total of 21 filters, 18 filters were installed horizontally over the canal by 15 specialists of Vietnam Environmental Incident Response Center Friday morning. An additional three were scheduled to be installed in the evening.

Each filter, 15-meters long and two-meters wide, was placed 100 to 150 meters apart. They are stabilized by floating rubber tops.

The filters were made by the center, said director Pham Van Son.

"The filters can block oil and chemical substances similar to oil," Son said.

The center has also collected oil-stained soil and vegetation along the canals in coordination with Vinaconex Water Supply Join Stock Company (Viwasupco), which processes and supplies clean water to around one million people in the southwestern part of Hanoi.

Son said dealing with oil spill incidents needs not be too complicated if proper cleanup procedures are followed.

Workers engaged in the oil cleanup at sections of the creek that feeds the Da River have said that they expect to work at least until this weekend.

The crisis began on Tuesday last week when a 2.5 ton tanker dumped used oil into a creek in Hoa Binh Province that feeds into the Da River, which Viwasupco sources water from to supply clean water to Hanoi.

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.

Two of three suspects were arrested on Friday for dumping used oil into the creek. The police are hunting for the third and investigating the roles of other people or organizations in the oil spill.