In the memory of fifty-six-year-old Li Yuexue, a local citizen of Kunming, capital of Yunnan province, the Dianchi Lake was once clean and rich in aquatic resources such as fish and shrimps.

However, since the 1980s, the lake began to deteriorate as the city expanded and developed at a fast pace. In the late 1990s, the lake became one of the most polluted in the country, and the water quality was deemed "inferior to Grade V," the worst level in China's water quality grading system.

The worsening situation aroused attention of the central government, which listed the restoration of Dianchi Lake a key project in fighting river and lake pollution across the country.

Cleansing the 36 major river channels including the Panlong River is just a basic step. Over the past 20 years, the city has built intensive underground pipes to intercept pollution and scores of large sewage treatment plants, where all wastewater has to be carefully processed before being reused or discharged into the lake.

Since 2013, large amount of water has been diverted into the lake to restore its self-purifying capabilities, amounting to about 3 billion cubic meters so far.

Du Jinsong is an engineer who has participated in Dianchi Lake protection project all the way. He said recovering ecology around the lake is also an integral part of the arduous undertaking. Now, thousands of hectares of wetlands have been established around Dianchi with relocation of some local residents, which form an important ecological barrier.

"They can effectively decontaminate the water before it flows into the lake," Du explained.

More than 50 billion yuan (around seven billion U.S. dollars) has been invested in the campaign during the past 20 years. Now the efforts have started to pay off.

In 2016, the water quality of the lake was upgraded to Grade V – a leap-forward in progress, and further improved to Grade IV in 2018.

"I can feel the changes. We can often spot fishes in the river now," said Li Yuexue.

Some rare animals like the glossy ibis and the garganey that used to inhabited here have come back. The lake area has also regained its status as the city's landmark tourist destination.

"Dianchi Lake is just a mirror of the economic and social development of Kunming. I believe we will brush up this mirror again and let the 'pearl' sparkle again with our persistent efforts," said Wu Tao, vice mayor of Kunming.