Sightings of blue-green algae in reservoirs in Guangdong Province have put local authorities on high alert to ensure the scourge does not contaminate the water supply, as it did this summer in Taihu Lake in Jiangsu Province.

"Blue-green algae has been seen in more than 20 reservoirs in the province," Li Yue'an, vice-director of the Guangdong water resource department, said at a water resource conference in the city of Shenzhen.

The algae comprise microscopic organisms that are naturally present in lakes and streams. Scientists have said they grow easily in polluted waters and an excess of them can starve the water of oxygen, killing fish and other aquatic life.

Li said if there is an outbreak of the algae in Guangdong, the effect will be worse than it was in Taihu Lake because of the higher temperatures and stronger sunlight in the province.

He did not say which reservoirs had been hit by the algae bloom.

Officials from the Guangzhou water resource bureau said the algae had not yet been detected in the city, the provincial capital. They said Guangzhou's rivers flow very fast, which helps counteract the growth of the algae.

Some experts have said it is unlikely Guangdong will witness a large-scale outbreak of the algae.

Li Jianji, director of the Guangzhou Astronomy Society, said yesterday that the region's Pearl River experiences at least two tides every day, which maintain the steady flow of the river and its tributaries.

Blue-green algae can only become abundant in relatively still water, he said.

The tides also carry large numbers of freshwater and saltwater fish to the mouth of the Pearl River, which eat the algae, he said.

"The river will not see an outbreak of blue-green algae in the next 10 years," Li said.

Han Boping, a hydrobiology professor at the Guangzhou-based Jinan University, who has studied the blue-green algae in the province for many years, said that local people and the authorities must, however, be on the alert for the algae once spring approaches and brings with it warmer temperatures.

He said the government should take measures to control pollution in rivers, lakes and reservoirs before the weather gets warmer.

In May, a blue-green algae outbreak hit Taihu Lake, affecting the water supply to thousands of people in Wuxi.

All About Blue algae, Water pollution

( China Daily December 28, 2007)