NANJING -- The Taihu Lake pollution crisis which affected the drinking water supply of about two million residents in east China has prompted local authorities to pledge more investment in sewage treatment and threaten polluting factories with closure.

"The city will monitor 22 key polluting companies and another 502 factories will need to be licensed to discharge waste," said Liu Hongzhi, vice mayor of Wuxi city in Jiangsu Province.

A bloom of algae in Taihu Lake caused the tap water supply to the city with a population of two million to be cut for days. The algae bloom had resulted from persistent water pollution from industrial and household sewage.

"New projects in the chemical, printing and dyeing and melting sectors in the downtown of Wuxi will no longer be approved," Liu said.

"The household sewage treatment rate will reach 75 percent by 2010 in both towns and counties in Wuxi," Liu said.

He also pledged that treatment of water pollution in Taihu Lake would account for three percent of the city's gross domestic product in 2010.

In Changzhou city, which has two rivers leading into Taihu Lake, 82 printing and dyeing, pharmaceutical and chemical plants have been ordered to halt the discharge of waste and limits on the amounts of waste were imposed on 18 other factories.

The dyeing and pharmaceutical plants who can not meet the waste discharge standards will be asked to cut their capacity by half, according to an emergency meeting of the Wujin District of Changzhou.

The quality of water from all tap water companies in Wuxi has met the standards for drinking water, after experts finally succeeded in dispelling the stench produced by the blue-green algae at Taihu Lake with potassium permanganate.

The tap water supply for Wuxi city was halted on May 22, when its major source, Taihu Lake, started to stink from a blue-green algae bloom.

Some 259 million cubic meters of water were diverted from the Yangtze River to dilute the lake.

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