BEIJING, June 5 (Xinhua) -- China's main environmental protection body has vowed to close all factories that are discharging pollutants into the Taihu Lake, which has been hit by an algae bloom contaminating the drinking water of two million people.

The bloom of blue-green algae in the east China lake was caused by natural factors and serious man-made pollution, said Zhang Lijun, deputy director of the State Environmental Protection Administration (SEPA), on Tuesday.

He told a press conference that the content of nitrogen in the lake in 2006 was three times of that in 1996, while the content of phosphate pollutants had increased by 1.5 times in the 1996-2006 period.

The algae bloom had stemmed from persistent water pollution from industrial and household sewage, helped by weather conditions in the area since April, Zhang added.

The algae in the Taihu Lake resulted in the suspension of tap water supplies to two million people in Wuxi City.

Workers have collected 6,000 tons of algae from the lake, according to an environmental protection official of Wuxi.