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.
'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.
However, "most treatment plants would not be designed to accommodate that level of shock loading. It's such an unusual event," he added.
Fyfe spoke in general terms about water quality issues, as he is not involved with Shanghai's water treatment.
"If they are chlorinating heavily, which a lot of places may do, especially if they've got a very polluted water body to start with, then the effects could potentially be small," Fyfe said.
Pig corpses that have been in the water for days would leak blood, intestinal fluids and other pollutants, which could alter the taste and color of tap water.
Many residents have begun drinking bottled water due to fears of contamination, according to the Global Times, a Chinese newspaper.