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.

Veterinarians from the provincial animal veterinary bureau in Sichuan province are trying to find out how the ducks died.

The bags of ducks found on the river were reported to the local environmental protection bureau on March 19. They were disinfected with lime and buried at a depth of 3 meters by local authorities a day later.

The carcasses did not pollute the river, the local environmental protection bureau said, and the incident will not threaten residents' water supply because there are no water plant intakes nearby.

Pengshan county is a major production area for duck meat, and the county's Baosheng township can produce more than 10 million ducks raised primarily for meat every year, according to the website of the animal veterinary bureau in Meishan city.

Raising such ducks can bring annual income of about 15 million yuan ($2.42 million) to 20 million yuan for local farmers, the bureau said.

Previously, more than 10,000 dead pigs were retrieved from the Huangpu River, a major source of tap water in Shanghai. Meanwhile, 50 dead pigs were found in a tributary of the Yangtze River in Yichang, Hubei province.

Experts have long called for more government efforts to regulate animal carcasses.

"The cases have shown that the knowledge and awareness of the disposal of animal carcasses is severely lacking among individual livestock breeders," said Ouyang Yan, a researcher on animal epidemic prevention at Hubei Three Gorges Polytechnic in Yichang.

To solve the problem, Ouyang said, the government should assess the capacity of animal farms to dispose of carcasses before granting approval for farmers to run them.

She said the government should provide subsidies to farmers for the disposal of carcasses to reduce risks from animal farms and to help authorities discover endemics as early as possible.

Xue Ruifang, a veterinarian in Pingding county, Shanxi province, writing in the Livestock and Poultry Industry Journal in November, said one local investigation found only 20 percent of animal carcasses are properly disposed of in rural areas.

"Individual pig breeders in rural areas generally do not know the harm caused by randomly dumping animal carcasses. They are also unwilling to spend money on such a problem," she said.

"A law that regulates the disposal of animal carcasses, especially in rural areas, is urgently needed right now."

The law should clearly define the penalties for randomly dumping or reselling animal carcasses and clarify who should take on the role of law enforcement, she added.

Huang Zhiling in Chengdu contributed to this story.

xuwei@chinadaily.com.cn