A blue-green algae bloom is threatening the water quality of a lake that provides drinking water for millions of people in the eastern Chinese city of Wuxi, Jiangsu Province.

Panic buying of bottled water and bread is occurring in Wuxi with a population of more than five million, after a blue-green algae bloom appeared on Tuesday in Taihu Lake and made the water smell unpleasant.

The price of an 18-liter bottle of water sold by street peddlers had risen from eight yuan to 50 yuan on Wednesday night.

Blue-green algae is a simple aquatic plant life that occurs naturally in rivers, lakes, damp soil, tree trunks, hot springs and snow. "Bloom" is the common term used to describe an increase in the number of algal cells to a point where they can discolor the water, form scum, produce unpleasant tastes and odors, affect shellfish and fish populations or otherwise create a nuisance and seriously reduce the water quality.

Initial investigations show the water level of Taihu Lake is at its lowest in 50 years this summer due to continuous high temperatures and lack of rain, which caused an excess of nutrients in the water.

The city government is planning to artificially induce rain on Thursday or Friday to dilute lake water, and the provincial government has agreed to divert more water from the Yangtze River to the lake.

Local authorities are closely monitoring the supplies of the bottled water in 10 supermarkets and have allocated more bottled water from neighboring regions.

Wuxi, administering six districts in the city proper and two other small cities, has a population of more than five million.

The affected population is mostly in the city districts, but the local government is still counting the exact number who have been affected by the blue-green algae bloom.

Local authorities are closely monitoring the water quality around the clock and Yang Weize, secretary of the Wuxi Municipal Committee of the Communist Party of China, vowed on Wednesday to guarantee safe drinking water "at all costs."