China ? Water supplies to 28,000 people in northern China have been cut after an overturned truck spilled 33 tons of toxic oil into a river, state media said, the latest mishap to degrade the country’s already polluted waterways.

The overloaded truck was carrying wash oil, also known as creosote, when it overturned and dumped its contents into a river in Shanxi province, Xinhua News Agency reported late Wednesday.

The spill flowed into the Yangjiapo reservoir, contaminating 70 million cubic feet of water, the agency said, citing the provincial environmental bureau.

Supplies to the towns of Dazhai and Sandu in Xiyang county, which the reservoir serves, have been cut, Xinhua said.

Creosote is commonly used to treat wood products and probably causes cancer in humans, according to the U.S. Agency for Toxic Substances and Disease Registry.

The spill occurred last Thursday, Xinhua said, but did not say why it was reported a week later.