Carcasses of thousands of pigs found in Shanghai's Huangpu River has heightened concerns about water pollution in China.

State-run Xinhua news agency reported Monday that 2,800 dead pigs were recovered by Sunday evening. Authorities said the pigs, which were first noticed last Thursday, may have been dumped from neighboring Zhejiang province.

The pig virus, porcine circovirus, had been detected in tests on one pig carcasses taken from the river, which is one of Shanghai's primary sources of drinking water. The Xinhua report noted that the virus cannot be transmitted to humans.

"So far, water quality has not been affected but we have to remove the pigs as quickly as possible and can't let their bodies rot in the water," Xu Rong, director of Shanghai's Songjiang District Environmental Protection Bureau, told the state-run Global Times newspaper.

China's water authority in a report last February said that up to 40 percent of the country's rivers were seriously polluted. Furthermore, it said that about 20 percent of China's rivers were so polluted the water quality was considered too toxic even to come into contact with.

"The deterioration of water quality has threatened the safety and health of people, while the water quality problem has limited the economic and social development and people's lives," Hu Siyi, vice minister at the Ministry of Water Resources said in releasing that report.

To draw attention to the condition of a polluted river, last month, a Chinese entrepreneur offered a pollution control authority official a $33,000 reward to swim in it. The official declined the challenge, which was posted on China's Twitter-like microblog service Sina Weibo and accompanied by photos of garbage floating in the river.

Groundwater is also a problem in China.

In a Sina Weibo post last month, activist Deng Fei accused aluminum smelters in Weifang prefecture of illegally pumping wastewater underground into pressurized wells.

In response, the Weifang government's environmental bureau conducted checks on more than 700 factories and maintained that none were pumping wastewater underground, the Financial Times reports. The bureau also established a hotline to report environmental violators, offering a reward to anyone who could find the illegal underground wells.

Still, Zhao Zhangyuan, an expert on water pollution at the Chinese Research Academy of Environmental Sciences told the Times, "Groundwater pollution has already entered a state of extreme crisis."

In 2011, the Ministry of Land and Resources published data indicating that 55 percent of 200 Chinese cities monitored had "poor or very poor" quality groundwater and that in 15.2 percent of sites tested the quality had declined from the year before.