An estimated 10,000 carcasses were found in the Huangpu River in Shanghai over the past two weeks, and another 4,600 upstream in Jiaxing, 100 kilometres further south-west, the Beijing-based Jinghua Shibao newspaper reported.
Eight farms have been fined for improperly disposing of carcasses by dumping them in the river, the report said.
The carcasses have prompted health concerns about water contamination, and the pigs' cause of death.
Authorities have assured the 23 million residents of the Shanghai urban area that the water supply, of which 20 per cent comes from the Huangpu, is safe.//DPA