The number of dead pigs fished out of Shanghai's main waterway has reached nearly 6,000, with local officials still puzzled as to how they ended up in the Chinese city's major source of drinking water.
State media on Wednesday reported the number of deceased swine found in the Huangpu River has doubled in two days, as workers continue to scan the waterway in search of carcasses.
Authorities in Shanghai, China's financial hub, say ear tags from the some of the pigs suggest they floated downstream from the neighboring province of Zhejiang, which has many pig farms. But Zhejiang animal husbandry and veterinary official Jiang Hao says this is not necessarily the case, since the ear tags only indicate where the pigs were born.
"We have a procedure for the labels on pigs' ears. After pigs are born, we tag the labels on their ears once they've been through the epidemic prevention process," said Jiang. "After they have been given a label, they might leave here and move somewhere else as they move around the market."
It is not clear how the pigs died, though some have tested positive for porcine circovirus, a common swine disease that does not affect humans.
Shanghai officials insist the dead pigs have not contaminated the city's water supply, saying the river is no more polluted than normal. The Huangpu River supplies nearly a quarter of the water for the city of 20 million people.
Water contamination, often caused by fertilizer runoff, chemical spills and untreated sewage, is a major problem in China. The government plans to spend $850 billion over the next decade to improve water supply systems.