Large areas of algae bloom in an upper Yangtze River tributary have forced thousands of residents in the central province of Hubei to stop drawing drinking water from the river.

The bloom first appeared on Monday in the Xiangxi River. By yesterday, it had expanded from five kilometers to about 23 kilometers, stretching from Gaoyang Township of Xingshan County to Zigui County, where it converged with the Yangtze River.

The river water has turned emerald green and opaque. Experts said excessive phosphate and a slow current in the river accounted for the phenomenon.

Local governments are closely monitoring the water quality and the spread of the algae and have advised residents against eating fish or drinking water from the river.

Blue algae choked east China's Taihu Lake last summer, triggering a drinking water crisis for residents in Wuxi City in Jiangsu Province.

Blue algae grows easily in polluted water with high concentrations of nitrogen and phosphorous and a temperature of about 18 degrees.

(Xinhua News Agency June 21, 2008)