China's environmental authority has warned of the imminent danger of a blue algae outbreak in Chaohu Lake, the country's fifth largest freshwater lake in east Anhui Province.

"The current conditions, including nitrogen and phosphorus contents in water, temperature, wind and sunlight, are favourable for the algae outbreak," said Lu Xiaoping, head of the provincial environmental protection bureau's water environment department.

Latest satellite pictures show that about 30 square km of the algae has gathered on the western part of the lake.

Lu said the current algae growth has not affected drinking water supply to local residents, since the water intake area is on the eastern side of the lake.

Chaohu is frequently hit by blue algae outbreaks between June and September. An outbreak in July last year suffocated 110 square km of the 700-square km lake area.

Environmental officials said that the algae nurtured mainly by pollutants of nitrogen and phosphorus is not poisonous, and can soon ebb under such conditions as wind, rainfall, or the heat with temperature rising above 37 degree Celsius. But its major harm is to suffocate the lake surface, killing aquatic animals and causing pollution.

Li Guanggui, a fisherman said only three to four fish in his daily hauls of over 5,000 grams were alive during the algae outbreak last year.

Li Zhaolin, a resident living by the lake side in the outskirt of Hefei, said the lake has smelled so bad since last week that he could not open his windows.

"The dead fish have brought swarms of mosquitoes, affecting the life here," he said.

Hefei City is the biggest polluter by the lake. The city discharged 21 million tonnes of industrial waste water into the lake in 2008, down by 70 percent from that of 2005, as the city has invested heavily on sewage treatment facilities after a serious algae outbreak caused drinking water problems in 2004.

In addition to the facilities, the city has also tried to put millions of algae-eating fish into the lake in the hope of fundamentally clearing the algae pollution.

(Xinhua News Agency June 30, 2009)