JIAXING, China -- Hard as it may be to believe, the recent discovery of thousands of pig carcasses floating in a river that supplies drinking water to Shanghai may represent an encouraging step forward in Chinese public health.
In May, for example, the police in this hog-producing city arrested four people who had sold dead pigs to slaughterhouses. And in December, a Zhejiang Province court sentenced 17 people to prison sentences, one for life, for processing and selling meat from pigs that had died of various diseases. In less than two years, the group had collected about 77,000 animals.
So, as the authorities have cracked down on people selling diseased or dead pigs, agriculture experts say, it is possible that someone may have decided it was better to dump dead pigs into the river.
If that was the case -- and there is no proof right now that it was -- a mystery remained: Where did the pigs -- 7,545 at last count, with the number still rising -- die, and who threw the carcasses into the Huangpu River?
After the pigs began showing up by the thousands in the river last weekend, teams of pitchfork-bearing men fanned out on barges to fish the rotting carcasses out of the water.
With food safety a growing concern in this country, and cities like Shanghai just beginning to enforce new rules that discourage restaurants from using recycled gutter oil, officials moved quickly to assure the public that the city's water supply met national standards, and that its pork supply was safe.
The city embarked on a major cleanup. Early this week, pig carcasses that had been dragged from the river were buried in deep trenches, and uniformed inspectors lugging suitcases filled with laboratory equipment tested pork samples at outdoor markets throughout the city.
The Ministry of Agriculture announced that it would undertake its own investigation.
One government department suggested that a likely explanation for the deaths was cold weather, even though the Shanghai area rarely gets snow and was in the midst of unusually warm temperatures last week.
The remark provoked ridicule on social networking sites, where some suggested that the comment was as ludicrous as believing that the pigs had engaged in mass suicide.
A more likely cause, porcine circovirus, a disease common among pigs but believed not to be harmful to humans, turned up in samples of the carcasses taken by the Shanghai authorities.
Jiaxing, which sits on the Huangpu River about 70 miles from Shanghai, was an obvious suspect as the source. Those suspicions seemed to be confirmed when Shanghai officials said that more than a dozen of the pigs carried ear tags indicating that they were from Jiaxing. The authorities then announced that they had detained a farmer who confessed to throwing his animals into the river.
But in Jiaxing, farmers denied dumping pigs into the river, calling it preposterous and saying that the animals could not possibly have floated all the way to Shanghai. "If we dumped pigs in the river near here, by the time they arrived in Shanghai, they'd be unrecognizable," said one farmer, Xu Jinfu.
Another farmer, Xu Jinhua, who was standing outside his pens with a shovel, said, "It feels a little uncomfortable to hear Jiaxing blamed for this." The farmer continued: "This river flows slowly. Do you think pigs from here would get all the way to Shanghai?"
Xu Jinfu, who helps manage a collective with about 3,000 hogs, said that piglets were often sold to farmers closer to Shanghai to raise, and that that may explain why some ear tags showed Jiaxing. Indeed, in photographs many of the dead pigs appeared to be relatively small.
He also said that Jiaxing had a designated disposal area for pigs that died of sickness.
Several other farmers in Jiaxing insisted that farms in the area had not experienced a high number of deaths or other problems, and that Jiaxing pigs were generally healthy.
"We treat our animals here well. We feed them well," said another farmer, Zhang Bing, who was pointing to large sacks of animal feed. "In Shanghai, they often just feed them table scraps. Those pigs are more likely to get sick."
Unscrupulous farm practices, though, are not uncommon in Jiaxing, or in other hog-producing areas.
Cracking down on food safety violations has not been easy. In 2007, the government executed the leader of the country's Food and Drug Administration for taking bribes from drug makers and failing to adequately protect citizens. The country also announced a nationwide crackdown on illegal food processors.
In Jiaxing, a local official named Huang Hao said one possible explanation was that the pigs had died while being transported to Shanghai, and that the truck drivers had simply dumped them in the river.
On a drive through Jiaxing, with a reporter following in another car, Mr. Huang stopped and pointed at a truck that was preparing a hog shipment. With three levels of cages stuffed with hogs, it was about to embark when Mr. Huang walked over and started pointing.
"Look! See how crowded this cage is? Look at that one, and that one," he said, pointing to hogs that seemed to be suffering beneath the weight of other hogs. "Some of those pigs will definitely die on the road!"
Three men finished loading the truck and locked the top level.
Not realizing he was a government official, the men largely ignored him and snapped back, "No, it's safe!"
Then the truck pulled away, and Mr. Huang shrugged his shoulders.
Xu Yan contributed research.
This article originally appeared in The New York Times.