Beijing, Aug 10 (IANS): Environment authorities in eastern China's Anhui province are battling an intense blue algae outbreak in Chaohu lake, the country's fifth largest fresh water lake, as they struggle to ensure clean water for local residents, the media reported on Monday.

Blue algae grew by as much as 852 percent from the normal level and it has been hard to contain, said Zhu Yu, deputy director of environment monitoring centre in Anhui.

The algae, which usually blooms in summer amid warm temperature, were found in the lake, the Global Times reported.

"We are closely watching the water quality. Microcystin, a toxin which threatens drinking water, has not been detected. We have also stepped up purifying procedure to ensure clean water supply," Zhu said.

Emergency water supply is ready, Zhu said. About 50,000 tonnes of water can be supplied from other water sources in ten days.

He Zequn, deputy director of environment protection department, said Chaohu's blue algae blight has eased over the last few years, but this year it has relapsed.

Over 220 million yuan (about $35 million) has been spent to contain blue algae this year.

About 120,000 tonnes of blue algae have been collected.

"The relapse is a new warning to us. We have to keep up the efforts," the deputy director added.