Shanghai environmental officials are cleaning up a river polluted by sewage in a suburban industrial zone.

The effort involves replacing an aged, broken pipe and injecting fresh water into Shanghengjing River, a major waterway in the Jinshan Development Park.

"A nearby sewage pipe linked to the drainage network which transports wastewater to a disposal factory was broken near the river, leaking untreated sewage into the waterway," said a Jinshan Environmental Protection Bureau official surnamed Zhang.

Residents who fish and wash clothes in the river first detected the pollution after the river turned dark and began to stink last week.

With the waste accumulated in the river during the summer heat, mud on the riverbed fermented to give off the smell and darken the river, Zhang said.