A Chinese farm admitted to dumping dead pigs into Huangpu River, which had about 6,000 bloated carcasses pulled from its water this week, state media reported.
The labels in the ears of the pigs indicated Jiaxing City as their birthplace, according to Xinhua, the Chinese state-run news agency. The city is south of Shanghai, in the Zhejiang Province.
Earlier, local Chinese media had suggested the dead pigs had come from the area with local officials blaming dumping on "local pig farmers who lack awareness of laws and regulations."
The city's government said a total of 70,000 pigs died from "crude raising techniques and extreme weather" at the beginning of the year, according to Xinhua. But it also insisted that the collected corpses were disposed safely.
The selling of diseased pigs appears to be a bigger problem in the area as on Wednesday, a court in Zhejiang Province, issued prison sentences for 46 people convicted of selling meat from diseased pigs, Xinhua said.
The sentences ranged from six months to 6 and a half years in prison, the report said.
Shanghai water concerns
The "dead pig dumping scandal" in Shanghai has been growing since Friday, Xinhua reported.
Chinese officials have said they expect to find more carcasses in the river -- but they insist the Shanghai water is fine.
The scandal has incredulous residents one-upping each other on the country's popular microblog service, Sina Weibo.
"Since when is finding dead rotting pigs in a major river not a public health problem?" Weibo user, @Muyunsanjun2011, asked. "Answer: When this happens in China."
A report in the Shanghai Daily newspaper earlier Wednesday said that no pollution had been found in the river.
"Since apparently, the water has not been contaminated, big leaders, please go ahead and have the first drink," Weibo user,@_Nina_Burbage quipped.
However, a later water sample was found to contain a porcine circovirus, Xinhua said.
The World Health Organization says there are two types of porcine circoviruses, but neither is known to cause disease in humans.
An official from a Shanghai water plant was quoted in Xinhua saying, "If the water is contaminated, we will put more the disinfectants and activated carbon to purify the water."
'Dead pigs all around'
Sanitation workers, clad in masks and plastic suits, have been fishing the bruised pig bodies surfacing in the Huangpu River. The pink, decomposing blobs have wreaked foul odors and alarmed residents.
"There were dead pigs all around and they really stunk," one local resident told CNN. "Of course, we're worried, but what can you do about it? It's water that we have to drink and use."
If the water treatment process is very effective and can handle the sudden glut of contaminants, it's possible to minimize the impact, said Julian Fyfe, a senior research consultant specializing in water quality at the University of Technology Sydney.