For 60 years, Bengbu's Soya Sauce Factory in Anhui province poured 100 tonnes of black, stinking waste water into the Huai River every day.
Three years ago it became one of the 6,500 factories along China's third largest river that were shut down during the country's biggest environmental clean-up.
Inspector Sun Yun of the city's Environmental Protection Bureau now comes two or three times a week to inspect the factory. 'A lot of small companies like this one have tried to reopen,' he said. 'It is difficult to stop them but if we catch them we fine them.'
About 150 million people live along the Huai River and its tributaries. Many of them have prospered through rural factories producing paper, leather, chemical fertilisers and other products.
Large state factories were given money to install water treatment equipment, but went bankrupt and shut down.
'We spent three million yuan [HK$2.8 million] on a water-treatment plant so we could reopen,' said factory manager Wu Dingan, showing visitors the tanks containing filters through which dark liquid bubbled.