And what does it say about China's water supply?

Over the weekend more than 2,800 dead pigs were fished out of the Huangpu River that bisects Shanghai--and is a source of drinking water for the city's 23 million residents.

The story highlights a seldom-covered source of China's water pollution problem: agricultural waste. Under Chinese law, farmers are required to take carcasses to their village or town's community disposal site, or bury the animals with disinfectant, but many don't. And as of 2010, agricultural pollution, which includes livestock and produce, surpassed industrial waste as China's main pollutant.

In fact, waste related to animals made up about 90 percent of organic pollutants in China's water, according to Wang Dong of the Chinese Academy for Environmental Planning. In a 2012 study from Huazhong University, waste from pigs, cattle, sheep, and other animals left 228,900 tonnes (252.6 tons) of biochemical oxygen demand, a standard measure for organic pollution, in part of the Han River in central China. Now, about 15 percent of China's major rivers are too polluted for safe use, not just from local factories, but farmers who throw animal carcasses and waste into nearby streams.

Chinese residents are well aware of the country's water pollution problems. A Chinese businessman recently offered a local environmental official 200,000 RMB ($32,000) to swim in a dirty river in Zhejiang province. The issue caught fire last month when investigative journalist Deng Fei invited people to post photos on Sina Weibo of polluted waterways in their hometowns.