Xie said the company sealed the source of the pollutant right after the accident occurred and appointed workers to monitor chemical spills by the river around the clock.

Xie's team was made up of more than 20 workers and three boats. The workers threw snow-white oil-absorbing sheets into the water to soak up the floating dirt, and three floating wooden barriers were installed in front of the sewage outlet to block the emulsion from pouring into the sea.

According to Xie, there was no more leakage from the factory, but the ebbing tide kept sweeping away the dirt left on the walls of the sewage pipe, making oil seepages offshore.

Zhu Hui, director of the environmental protection bureau of Mawei district, said the pollution was under control by 5 pm on Wednesday and the river has been substantially cleaned.

He blamed the company for not immediately reporting the accident to the local environmental protection authorities, which received reports from the public the next day.

Zhu said daily tests of the water quality showed that pollutants exceeded standards when the accident happened but gradually eased and will not endanger aquatic animals.

But the crisis has made residents question the credibility of the company, which claimed "zero discharge" of wastewater because of its 20 million yuan ($3 million) investment in a waste treatment facilities.

"I almost shed tears when I saw the river covered by a thick layer of gray and black grease on Tuesday morning," said Zhang Muxing, a 56-year-old resident who works at the Yuanyang Fishing Berth, only 400 meters from the sewage pipe outlet.

Zhang said he has been working at the site for 30 years, and oil spills on the water surface were seen from time to time after the factory went into production in September.

"As a resident, I worried a lot about our health, as the pollution caused by an irresponsible enterprise might put local residents under the threat of toxic drinking water," he said.