East China's Wuxi city will spend at least 4.5 billion yuan (684 million U.S. dollars) this year tackling pollution in algae-plagued Taihu Lake, city environment authorities said Wednesday.

Taihu, China's third largest freshwater lake, has suffered rampant blue-algae growth in the past 10 years, due to sewage discharges as well as industrial and agricultural waste.

Water quality had improved after the city government spent about 30 billion yuan in the past four years to clean up the lake after an algae outbreak in May 2007 rendered tap water undrinkable for more than a million residents in Wuxi, Jiangsu Province.

However, Taihu remained vulnerable to algae outbreaks, especially in warmer weather, as the water was still not completely clean, said a spokesman with the lake's pollution control office Wednesday.

The investment this year would be channeled into hundreds of projects to cut pollution discharges, ensure the safety of drinking water and restore the lake's ecosystem, he said.

The lake, covering 2,400 square kilometers, is a major source of drinking water for more than 30 million residents in Jiangsu and neighboring Zhejiang Province and Shanghai Municipality.

Local governments have tried to close polluting factories around the lake, set up sewage treatment plants, and dredged up nutrient mud from the lake to curb pollution and stop the algae blooms.