Yuan Aiguo, a professor with the China University of Geosciences, told Xinhua news agency that authorities should pay urgent attention to the pollution woes in the Yangtze, which is China's longest river and third longest in the world.

"Many officials think the pollution is nothing for the Yangtze... but the pollution is actually very serious," said Yuan, while Xinhua described the state of the water as "cancerous".

Liu Guangzhao, another scientist, was quoted as saying the Yangtze was in danger of becoming a "dead river", with many plant and animal species already disappearing.

There were 126 animal species living in the Yangtze in the mid 1980s, but the number was down to 52 by 2002 due to the pollution, he said.

Environmentalists believe a combination of industrial and agricultural discharges, along with sewage and ship waste, are to blame.

Lu Jianjian, a professor with the East China Normal University, told Xinhua the Yangtze absorbed about 25 billion tons of waste water a year -- more than 40 percent of the country's total.

More than 80 percent of this waste water entered the Yangzte untreated, said Lu, who is a member of the Chinese People's Political Consultative Conference, the country's parliamentary advisory body.

Lu warned the citizens of Shanghai and many other cities, which are dependent on the Yangzte for their drinking water, were being placed at risk.

More than 500 pumping stations are located on the Yangtze's banks to draw drinking water, Xinhua reported. Some of the stations have been moved midstream in an effort to avoid the worst of the pollution at the river's edges, it said.

The Yangtze stretches 6,300 kilometers (3,906 miles) from the northwestern province of Qinghai and traverses through 186 cities, including Shanghai, before emptying into the East China Sea.

More than 70 percent of China's rivers and lakes are polluted, while underground water supplies in 90 percent of Chinese cities are contaminated, according to previous state press reports.

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