The city government has set aside ten million yuan to combat an outbreak of blue-green algae in Xinlicheng reservoir that provides water to the city, a government spokesman announced on Wednesday.

Swathes of blue and green algae began to appear last Wednesday in Xinlicheng Reservoir, one of the city's major water sources for 100,000 residents.

On Tuesday, the water supply from both Xinlicheng and Shitoukoumen Reservoir was cut off. The supply from Xinlicheng has been shut off indefinitely but the local environmental authorities ruled that Shitoukoumen had not been affected.

Changchun used 770,000 tons of water per day before the outbreak of blue algae but the daily supply has plunged by 50,000 tons since the Xinlicheng reservoir water source was cut.

Changchun mayor Cui Jie said the ten million yuan would be spent on expanding pipes linking the city to the reservoir of Shitoukoumen, and transporting water with fire engines.

"We must do our best to ensure the drinking water supply for our citizens," said Cui, adding that he was considering closing car washes.

Recent outbreaks of blue-green algae in key lakes in eastern and southwestern China are mainly attributed to pollutants from chemical factories, but this time the finger is being pointed at agricultural fertilizers.

The algae may have been caused by fertilizers and pesticides from nearby cropland, local authorities say.

High temperatures and scant rainfall since June also contributed to the algae bloom and recent downpours have nourished the algae.

Changchun is home to a population of more than seven million, with 2.7 million living in the downtown area. The reservoir has a water storage capacity of 592 million cubic meters.

In the last two months, blue-green algae outbreaks have been reported in Taihu Lake, Chaohu Lake and the southwestern Dianchi Lake, endangering water supplies.

On July 4, water supplies to 200,000 people in Shuyang county, Jiangsu Province, were halted for more than 40 hours after ammonia and nitrogen were found in a local river.