WUHAN, June 7 -- With four months to go before the middle route of China's ambitious south-north water diversion project opens, pollution control and water quality protection efforts are well underway.

On Thursday, 10 million fish fry were released into Danjiangkou Reservoir, a major water source along the route, in central China's Hubei Province.

"These fry will contribute to the reservoir's biodiversity and help keep the water clean. It is a good method of water treatment as there's no side effects," said Xie Shouqi, deputy director of the Institute of Hydrobiology under the Chinese Academy of Sciences.

Release of fry into the Yangtze has been an annual event for over a decade to protect fish resources and maintain the ecosystem along the river.

The Danjiangkou Reservoir was chosen as the place to release the fry this year to draw attention to the water source , said Niu Dun, vice minister of agriculture.

The water diversion project was first envisioned by Mao Zedong and is designed with eastern, central and western routes. It will eventually cost an estimated 500 billion yuan (81 billion U.S. dollars) and take 40 to 50 years to complete. The project will carry around 45 billion cubic meters of water annually from the wet south, mainly the Yangtze River reaches, to the dry north.

Construction of the eastern and middle routes began in December 2002 and December 2003 respectively. Water from the middle route will go mainly to Beijing.

By 2015, China plans to invest 12 billion yuan in sewage and garbage treatment facilities, soil conservation, and on treating polluted rivers, agricultural pollution and mine tailings around the Danjiangkou Reservoir.

So far, over 1,000 factories have been shut down in the provinces of Hubei, Henan and Shaanxi with some positive effects. Water quality in the Danjiangkou Reservoir has reached grade II, the mandatory standard for the project, while the water in some areas has even reached grade I. Level of nitrogen and phosphorus in the water are still too high.

China grades water quality according to six levels: grades I to V and "inferior to Grade V". Water below Grade III is not safe to drink.

Though the water quality in Danjiangkou Dam has been improved to meet the standard for transfer, there are still many factors, including mining, overuse of fertilizers and discharge of untreated waste, that can easily derail the efforts. The country and local governments still face an arduous battle to ensure the water transferred to Beijing is clean enough.

Wang Hao, an academic with the Chinese Academy of Engineering, called for the introduction of a compensation mechanism and the development of green agriculture as a long-term solution to these problems.

"A compensation mechanism is both necessary and feasible to urge the northern regions fulfill their responsibilities to support environmental protection while the local people living around the water source must be compensated for the economic opportunities they have given up for water conservation," Wang added.