Large patches of of blue algae have appeared on the Chaohu Lake in east China's Anhui Province, China's fifth largest freshwater lake, local environmental authorities said.

But that does not affect drinking water supply to local residents, the authorities said.

According to an official with the Anhui Provincial Bureau of Environmental Protection, about 13 square kilometers of blue algae has appeared in the western part of the lake.

A report from the provincial environment monitoring center said the lake had been heavily polluted by nitrogen and phosphorus in the past five months.

In such circumstances, the blue algae can break out at any time, and it is impossible to eradicate it in a short period, said bureau vice director Yin Fucai.

Yin, however, said that the algae has yet to affect the drinking water in Hefei and Chaohu, two major cities along the lake that measures about 800 square kilometers.

He explained that Hefei's drinking water relies on two reservoirs near the city, and Chaohu City draws water from the eastern part of the lake.

Even if the blue algae spreads to the east, said Yin, people in Chaohu City can resort to water diverted from the Yangtze River.

The bureau has been closely monitoring the lake since June when the weather became scorching, and collected data every two days.

Chaohu lake experienced a blue algae bloom in July 2004 but it soon ebbed after timely winds and rainfall.

(Xinhua News Agency July 19, 2008)