A man sits by the bank of a river in Beijing which is polluted with blue-green algae on Wednesday, July 18, 2007. [Photo: thebeijingnews]

Beijing Water Authority said on Thursday minor algae blooms have been found in some water areas in the capital, and warned the city faces risks of algae outbreaks.

Zhang Shiqing, director of the authority's rivers and lakes department, said about 100 square meters of algae blooms have been found in water areas of Chaoyang district in eastern Beijing and the Summer Palace in the capital's northwest.

The algae blooms were triggered by poor ventilation and slow water flows, he said, adding that the algae had been cleared.

Nine other water areas, including Houhai, Yuyuantan lake and the Bayihu lake, are also prone to algae blooms, he added.

Zhang said the conditions were right for algae blooms. "There has been scant rainfall this year to dilute the water, some of which was already polluted by garbage. The summer heat is also helpful."

Statistics with the authority show Beijing is home to 118.39 kilometers of rivers with 8.66 million square meters of water area.

He said the department has cleared 27,000 cubic meters of garbage and silts from water areas. It also introduced water lilies, snails and shellfish to boost biological diversity, and catalysts and chlorine to purify water.

Eighteen monitoring stations had been set up, he added.

Algae blooms in rivers and lakes were unlikely to affect water supplies in the city, as the major water sources were underground water and reservoirs in suburban Miyun and Huairou districts, Zhang said.

Algae blooms are usually formed in water that is rich in nutrients, when the number of algal cells increase to a point where they discolor the water, form scum, produce unpleasant tastes and odors, and seriously reduce water quality.

In the last two months, blue-green algae outbreaks have been reported in Taihu Lake, Chaohu Lake, the southwestern Dianchi Lake, and a reservoir that provides water to Changchun, capital of northeast China's Jilin Province, endangering domestic water supplies.