More than 2,000 dead pigs have been found in one of Shanghai's main water sources, triggering fears of potential water pollution.
Chinese authorities said they began receiving reports of the animals floating upstream in the Huangpu River last week.
Environmental experts worked during daylight hours on Sunday to retrieve them, but stopped overnight due to safety concerns.
Xu Rong, director of the Songjiang environmental department, said: "We have been picking up dead pigs from morning to night.
"We cannot do it at night due to safety concerns. We cannot work (all) night, so we usually start (work) at around 6:30am and continue until dark."
Officials have begun investigating where the pigs came from.
So far they have found no evidence they were dumped into the river or that there has been some sort of animal epidemic, Shanghai's agriculture committee said.
Test results have indicated that so far the quality of water from there has not been affected.
However, to ensure tap water safety, authorities said they had strengthened the examination and disinfection process.
One local resident claimed pigs could be seen in the river "every day" but admitted "the number is much greater than those in previous years".
Some reports said the pigs may be from a farm in Zhejiang Province.
