BEIJING, July 31 -- Shanghai's Fengxian District water and police officials are still investigating an unidentified yellow liquid that has polluted a pond, a creek and a canal in the district, forcing the closing of one water plant as a precaution.

    District water officials said the liquid was found in Guyue Pond, Beixin Creek and Punan Canal since July 12.

    Punan Canal is the major water source for the Zhuanghang Town Water Plant. The plant was closed on Wednesday after some residents complained on Tuesday on the local environmental protection hotline 12369 that the Punan Canal might be polluted.

    Environmental inspectors said they found a yellow belt about 2.5 kilometers long in the canal that was expected to reach the plant's water intake, about 1 kilometer away.

    The plant produces 10,000 tons of water per day and serves 3,000 families and businesses at Zhuanghang Town, a water plant official said.

    Water supplies to these users were not affected as Fengxian No. 2 and No. 3 water plants are serving affected customers, the official said.

    Water officials said the pollutant has not tainted any drinking water supplied to local residents, because none of the polluted water reached the intake of the water plant.

    Officials are investigating the possibility that someone might have dumped the material into the bodies of water at night.