A new algae outbreak could affect China's Taihu Lake, which supplies water to about 30 million people, as scattered algae belts have been detected, officials said on Wednesday.

Sporadic swathes of blue-green algae have been found in some southern parts of the lake, China's third-largest freshwater lake, but water intake sites have not been affected, the Taihu Basin Administration said.

The administration, which is under the jurisdiction of the Ministry of Water Resources, said an inspection on April 9 and 10 showed water quality near water intake sources was stable and water supplies were normal.

An algae outbreak in late May 2007 rendered tap water undrinkable for about 10 days, affecting more than one million residents in Wuxi City, Jiangsu Province. Jiangsu, Zhejiang and Shanghai get much of their water from Taihu.

Qin Boqiang, a researcher with the Nanjing Institute of Geography and Limnology, part of the Chinese Academy of Sciences, said satellite monitoring showed blue algae began to appear in the west and south of the lake on April 3, showing that the lake had entered a sensitive period of annual algae outbreaks.

Jiangsu has stepped up emergency monitoring by provincial, city and county agencies and demanded better pollution control efforts.

Workers in Wuxi City have removed 190,000 tons of blue algae and one million cubic meters of silt from the lake, according to the local government.

High levels of nitrogen and phosphorus are believed to be major causes of algae outbreaks, which develop in water that is rich in organic matter.

(China Daily April 17, 2008)