An estimated 250,000 tonnes of fish died in a river in central China’s Hubei province overnight, with fishermen saying polluted water from a pig farm upriver could be to blame, the report said on Thursday.

It said that most of the fish were raised by fishermen inside large floating cages in Shanfong fish pond in a river in Jiangli County.

“100 per cent of the fish have died,” a fisherman said.

The fish farm had 33 cages and total losses could reach 1.6 million dollars, the fishermen said.

Polluted waterways are a major problem in China.

In the spring of 2013, an estimated 10,000 dead pig carcasses were found in Shanghai’s Huangpu River over a period of two weeks, with another 4,600 carcasses found upstream in Jiaxing, 100km further south-west.

While China has almost 20 per cent of the world’s population, the country contains only 7 per cent of the world’s freshwater.

At least one-third of China’s lakes and rivers are unfit for human use, according to a recent study by the International Water Association.