Dianchi Lake is 40 km long and eight km wide with a water storage of 1.5 billion cubic meters. It is the major source of water for industrial and agricultural use in Kunming, capital of Yunnan, and also plays a key role in balancing the city's environment.

"The lake was pure and clear in the early 1980s. I used to swim in the lake in summer," said Li Jie, a man who lives by the lakeside. "But even fish are seldom seen there now, let alone swimmers."

The lake became murky because of the industrial and domestic waste discharged into it over the past 20 years.

The pollution grew steadily worse after 1990. The lake surface is covered with a layer of blue green algae caused by an influx of waste water containing nitrogen, phosphorus and other harmful substances.

In 1995, the central government decided to clean the country's three rivers and three lakes including Dianchi Lake in an effort to reduce by 10 percent within four years total discharges of nitrogen and ammonia into those waters.

Yunnan has invested 6 billion yuan (722 million US dollars) to dredge the lake bed, clear up algae, build sewage disposal plants and close 249 enterprises discharging pollutants.

Though the water deterioration has been checked, the quality is far from satisfactory. It would take 20-30 years to make the lake water as clear as it was in the 1950s, said Xu Haiping, deputy director of the Yunnan Provincial Institute of Environmental Science.

He Bin, director of the institute, suggested the province import advanced pollution control techniques from abroad, ban the use of products containing phosphorus from around the lake and gradually replace polluted water with clean water.

(Xinhua News Agency November 11, 2002)