Chaohu Lake, one of Shanghai's major water sources, has become highly polluted after torrential rains fell in eastern Anhui Province.

Three of the nine rivers that border the lake were reportedly heavily contaminated, while the water quality of the other six was described as mildly polluted or intermediate.

An official with the water environment protection office under Anhui Province, who only gave his surname as Lu, said that flooding had caused the contamination.

"August floods in the area caused fertilizers that were not absorbed in nearby fields to enter the lake, increasing the phosphorous levels in the water," he said.

"Chaohu Lake has low motility and has not been able to sufficiently dilute (the chemical)."

Lu said that the city of Chaohu, which is on the eastern side of the lake, was not affected by the pollution. Although it depends on the lake for its water supply, he said that the intake point for the city's water supply was sufficiently far away from the worst contamination.

He said that local government officials haven't yet found an effective measure to solve the problem.

"The lake is not deep and mostly enclosed, making dilution more difficult," he said. "And we have not invested enough money (to deal with the situation)."

Duan Liping, from Chaohu, said that tap water had a bad smell about two or three weeks ago but improved after it was treated with chemicals.

"We've got used to pollution," she said.

The lake became polluted in the 1980s as nearby cities began to develop, Lu said.

"Factories were established and waste was not properly handled before releasing it into the lake."

"It was only after 1995 the city began to process domestic sewage."

Lu said that the provincial capital of Hefei changed its water supply from the lake to the Yangtze River due to pollution.

He said that there had been efforts to clean up the river and there had been improvements, "but there is still much to be done."

(China Daily September 6, 2007)