China explores using fish to tackle water pollution in Three Gorges Reservoir

China has begun the second phase of a research project to explore the use of fish to clean up water pollution in the Three Gorges Reservoir on the Yangtze River, the country's largest river.

China Three Gorges Corporation, operator of the world's largest hydroelectric station at the Three Gorges Dam, has released 600,000 fish into the Gaolan River, a tributary of the Three Gorges Reservoir.

The company said Tuesday that it sought to determine how well silver and bighead carp could clear algae blooms and improve the water environment while learning more about these efficient algae-eating fish.

The first-phase test, between 2008 and 2009, showed certain kinds of fish did help prevent algae outbreaks in the highly polluted Gaolan River.

The algae blooms in the Three Gorges Reservoir have long been under the spotlight. Some of its waters were polluted due to rapid developing agriculture and industry along the river, said officials.

The move came as the Chinese government decided to take effective measures to curb the environmental deterioration in the Three Gorges Project areas by 2020, said a statement released after an executive meeting of the State Council last week.

The world's largest hydroelectric project has played a significant role in flood prevention, power generation, shipping and water resources use, the statement added.

While at the same time there existed problems concerning the well-being of relocated residents, environmental protection, and geological disaster prevention that should be resolved urgently, it said.

It further stressed the need to curb water pollution in the middle and lower reaches of the Yangtze River, which affects eight provinces with an area of 633,000 square km. The area is also the nation's most densely populated, which means it coexists among significant environmental pressures.

Zheng Shouren, a main Three Gorges Project designer and chief engineer of the Yangtze River Water Resources Committee, said the designers were aware of some of the ecological problems as early as when the construction designs were under deliberation.

"We've been taking measures to tackle the problems during these years and the efforts have yielded marked results," Zheng said. "Also some problems are not as severe as expected," he added.

The silt accumulation in the Three Gorges Dam since 2003, when water levels were raised to 135 meters, for example, was only 40 percent of the design level, with an annual accumulation of less than 200 million tonnes, data from China Three Gorges Corporation showed.

As the Three Gorges Reservoir stored water, problems like algae outbreaks and floating garbage occurred, and they attracted widespread attention, Zheng said.

"They are all world-wide problems which all major reservoirs face," he said. "Given the limitations of current conditions and methods, we can only try resolving these issues."

"Some problems even come with economic and social development. When we made the designs, we didn't expect China's economy to grow so fast," he said.

The reservoir was designed to discharge 5,000 square meters of water per second downstream after October each year, but now the discharge has been raised to 8,000 to 10,000 square meters per second, as the designed volume failed to meet the demand of the lower reaches hit by severe drought, he said.

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