Tens of millions of algae-eating fish, voluntarily donated by residents in the nearby four cities, have been released over the past two days into Taihu, China's third largest freshwater lake, to curb algae growth.

The 2,400-square-km lake in east China is a major drinking water source for the 17 million residents that lived around the lake. Blue-green algae choked the lake in 2007, considerably reducing drinking water supplies.

Residents in four cities surrounding the lake -- Suzhou, Wuxi, Changzhou and Huzhou -- voluntarily donated one million yuan (US$146,200) to buy algae-eating fish, such as silver carp and grass carp, and released them into the lake.

Among the volunteers, children from a primary school in Huzhou donated more than 10,000 yuan with all the coins they collected. It took a bank clerk three hours to count the money which weighed some 10 kg.

Ding Yujia, 11, said she often heard mother describe the lake as clean and beautiful. "One day I will be able to see a Taihu Lake that once only existed in my mother's memory."

Blue-green algae, which exists widely in water bodies and is not harmful itself, grows easily in polluted water with a high concentration of nitrogen and phosphorous and a temperature of around 18 degrees Celsius.

An excess of blue-green algae removes oxygen from the water, killing fish and other aquatic life, which then decay and release toxin.

Wang Xiaolin, an official with the Taihu Lake Fishing Administration, told Xinhua, on March 5 the Jiangsu provincial government also bought some 65 kilograms of silver carp to put into the lake.

A silver carp could consume 50 kg of algae and other plankton life in the course of gaining about 1.5 kg in weight. Researchers estimated that it would take 100 million fish to clean the lake.

A 42-year-old fisherman Qian Fenglin said, "actually there have always been algae in the lake. But in the past there were also many fish and shrimp that could eat the algae. In the recent years, we caught less fish and the algae started to boom."

Earlier reports said many sewage pipes were built to prevent direct sewage discharges into the Taihu Lake Basin, but the pollution of the water remained a major problem.

An official with the Huzhou Environmental Protection Bureau said, "maybe those algae-eating fish cannot eat up all the algae, but they do raise the public awareness about environmental protection."

(Xinhua News Agency March 7, 2009)