Chinese state media says the number of pigs collected from a river near the city of Shanghai has risen to 5916.
The Huangpu river is a source of drinking water for the city of more than twenty million people, but officials say water quality there has not been affected.
The BBC reports that laboratory tests of one water sample had found traces of porcine circovirus, which can spread among pigs but not to humans.
It is believed that the pigs may have come from Jiaxing in the neighbouring Zhejiang province, although the cause of their deaths is still not clear.
In a statement, the Shanghai municipal government said that the water in Huangpu River, which is a major source of drinking water for Shanghai, was safe. It also said that no diseased pork had been detected in markets.
But the news has been met with scepticism by some users on weibo, China's Twitter equivalent, where the hashtag "Huangpu River dead pigs" has emerged.
"Cadres and officials, we are willing to provide for you, but please don't let us die from poisoning. Otherwise who will serve you? Please think twice," said netizen Shi Liqin.
"This river's colour is about the same as excrement, even if there weren't dead pigs you couldn't drink it," said another, with the username Yuzhou Duelist.
The Government statement said that the number of pigs being salvaged from the river appeared to be decreasing.