Local authorities are investigating how more than 1,000 rotting ducks ended up in a river in Pengshan county, Sichuan province, days after thousands of dead pigs were retrieved from a Shanghai river.

The dead ducks, found in up to 60 woven plastic bags, are believed to have been washed downstream into the Pengshan section of the Nanhe River, said Liang Weidong, deputy director of the publicity office of Pengshan county.

"The bags were scattered over a wide area of the river. That is a clear indication that they have been washed down from upstream," Liang said.