The water supply of at least two cities in central China has been affected by the emergence of yellow algae in a major river after days of lower than normal water levels due to recent low rainfall.

The large amount of algae began to emerge in the filtering ponds of three plants of the state-owned Zhonghuan Water Company. The build- up led to frequent blockages in the ponds, according to the Xiangtan City-based company in Hunan Province.

The filtering ponds are normally washed every 24 to 36 hours but under the current serious conditions they have to be washed every two hours, said Yuan Cheng, Zhonghuan Water Company's deputy general manger.

Large areas of algae are visible in the section of Xiangjiang River passing through Xiangtan.

Yuan said the city was experiencing water shortages and its urban Hedong District only had half its usual supply. Apartments in high-rise buildings were suffering from low pumping pressure.

Hunan's main Xiangjiang River water level hit a record low of 26.82 meters at 8:00 AM on Friday in Xiangtan, 0.04 meters under the previous low.

The combination of the low water level, its high content of ammonia and nitrogen, and the high temperatures in recent days had contributed to the algae outbreak, according to experts.

Algae was also affecting water supplies downstream in Zhuzhou City. Monitoring by local environmental authorities showed the amount of algae was 10 times greater than usual, affecting the city's water purifying plants.

The plants had increased the amount of chlorine used to clean the water.

Polluting factories along the river were being closed in several cities including Changsha, the provincial capital.

Two hydroelectric facilities, one upstream and the other midstream, began to discharge more water downstream at 8:00 AM on Friday, according the Hunan Provincial Flood Control and Drought Relief Headquarters.

(China Daily October 26, 2008)