Chinese experts on Monday warned that the country's longest river -- the Yangtze -- is "cancerous" with pollution, which is threatening the safety of drinking water in cities on its banks, including Shanghai.

The pollution in some sections was getting worse and would become another heavily-polluted Yellow River or Huaihe River in five to 10 years if no action was taken, Lu Jianjian, a professor with the East China Normal University, told Xinhua.

As the river was the only source of drinking water in Shanghai, it had been a great challenge for Shanghai to get clean water, said Lu, also a member of the National Committee of the Chinese People's Political Consultative Conference, the country's top advisory body.

Other cities along the river face similar risks in drinking water safety, experts say.

More than 500 pumping stations are located on the Yangtze's banks to draw drinking water, and some have to be moved midstream due to the worsening pollution near the edges.

Lu said the Yangtze River absorbed more than 40 percent of the country's waste water, about 25 billion tons a year, with more than 80 percent of the wastewater entering the Yangtze untreated.

Yuan Aiguo, a professor with the China University of Geosiences, urged authorities along the river to pay more attention to the worsening pollution of the Yangtze River.

"Many officials think the pollution is nothing for the Yangtze, which has a large water flow and a certain capability of self-cleaning, but the pollution is actually very serious," said Yuan.

Just 31 percent of the water is of first or second class quality, with 35 percent under the third class. Yuan warned that with no measures taken to curb pollution it was possible the river would have 70 percent water below the third class in three to five years.

Liu Guangzhao, a Chinese-Australia scientist, told Xinhua that if 70 percent of water dropped to the fourth or fifth class, many hydrophytic plant species would disappear and the river would become a dead river.

Professor Lu said that 126 animal species lived in the Yangtze in the mid 1980s, but the number was down to 52 by 2002 due to the pollution.

Environmentalists believe there are three major reasons for the worsening pollution: industrial wastewater and sewage; agricultural pollution; and ship waste.

Of the 16.75 billion tons of wastewater that flowed into the Yangtze in 2004, industrial waste was 7.66 billion tons, while domestic wastewater was 9.09 billion tons.

Experts estimated that chemical fertilizers, pesticides, and other agricultural wastes accounted for one third of the pollution.

Every year about 210,000 ships run on the river, discharging about 360 million tons of oil-contaminated wastewater and sewage, in addition to 75,000 tons of other waste.

Little progress had been made despite more than 170 wastewater treatment plants being built along the Yangtze, experts said.

Quite a few localities along the middle and lower reaches, ignoring the damage to the river, are still running pollution-causing paper-making, shipbuilding, heavy chemical and steel plants along the river.

Lu urged the local governments to take necessary measures on pollution treatment immediately, so as to prevent the river system being destroyed.

The longest river in China and the third longest in the world, the 6,300-kilometer Yangtze starts at the 6,621-meter snow-covered Geladandong, the main peak of the Tanggula Mountains in northwestern Qinghai Province.

It flows through Qinghai, Tibet, Yunnan, Sichuan, Hubei, Hunan, Jiangxi, Anhui, Jiangsu and Shanghai, where it empties into the East China Sea, passing 186 cities. The economy along the Yangtze valley accounts for more than half of China's total.

(Xinhua News Agency May 30, 2006)