The coal tar sludge spilled from an overturned truck has only flowed 1.5 km down the Dasha River in north China in 42 hours thanks to all-out cleanup efforts, officials said Sunday.

The sludge was 52 km away from a downstream reservoir in Fuping County, Hebei Province at 5 a.m. Sunday, said the officials with the local environmental protection bureau.

A overloaded truck carrying 80 tons, formerly 60 tons as told by the officials, of coal tar overturned in Fanshi County in Shanxi Province on Monday and spilled part of its load into the Dasha River, which originates from Shanxi, passes 80 km to Fuping.

The polluted session of the river turned brown and smells irritant even from tens of meters away.

Cleanup workers have built at least 51 dams along the river to intercept the spill amid measures to minimize the pollution threat to the Wangkuai Reservoir, a drinking water source for 10 million people in Hebei and also a standby for the Beijing 2008 Olympic Games.

Fuping cleanup workers succeeded in building a major dam of 370 meters long, 5 meters high and 20 meters wide on Saturday morning, which is able to contain 200,000 cubic meters of water.

Fifty-three tank cars have pump out 1,700 tons of polluted water since the dam was built.

The local governments of Fanshi and Fuping have made all-out effort to prevent the spill from entering the reservoir. Over 100 dredging machines and 100,000 people in Hebei have been mobilized to build dams and conduits to slow down the sludge flow.

Activated carbon, cotton quilts and sponge have been thrown into the river to absorb the coal tar.