KUNMING, June 16 (Xinhua) -- Though Liu Fanjun's memory sometimes fails him these days, the 73-year-old can still recite a nursery rhythm about a lake in his hometown in southwest China's Yunnan Province.

"Dianchi Lake stretches far into the sky with clear water sparkling in a boundless width. Row your boat, dance with fish and happily return home after sunset," Liu hummed.

Located in Kunming, capital of Yunnan, Dianchi Lake is the largest fresh water lake on the Yunnan-Guizhou Plateau, covering more than 300 square kilometers.

Known as the "sparkling pearl embedded in highland," Dianchi Lake is the major source of water for industrial and agricultural use in Kunming and also plays a key role in balancing the city's environment.

"Fishermen walked home along the tranquil lake before sunset. Children swam in the lake on hot summer days. These are my memories of the lake," Liu recalled.

The picturesque scenes changed in the late 1980s when the lake became murky because of the industrial and domestic waste discharged into it. The lake surface was covered with a layer of blue green algae caused by an influx of waste water containing nitrogen, phosphorus and other harmful substances.

"More and more untreated industrial waste and agricultural fertilizer was dumped straight into the lake," said Liu. "White foam along with rotten fish and shrimp piled up along the lakeside."

In 1990s, water quality in the lake was once deemed "inferior to Grade V," the worst level in China's water quality grading system and "too polluted for any purpose." About 80 percent of local fish species in the lake disappeared.

To protect Dianchi Lake, the central government and Yunnan provincial authorities then implemented a series of measures to restore its lost splendor after decades of severe pollution.

Kunming has built nearly 100 kilometers of pollution interception pipes along the bank of the lake to prevent waste water from entering the basin.

As much as 566 million cubic meters of water are diverted into the lake every year since 2013 to restore its self-purifying capabilities. Several waste water treatment plants have been built in 20 towns and 885 villages in the vicinity.

In 2008, Yunnan began to appoint "river chiefs" with responsibilities which include water protection, pollution prevention and control, as well as ecological restoration in the basin.

Fishing was also prohibited in the lake throughout 2010 and 2011, according to Wu Chaoyang, deputy director of Dianchi Lake administration bureau.

Earlier efforts have already begun to pay off. Water quality in the lake rose to grade IV in the first quarter of this year, a testament to what Yunnan has achieved.

In March, garganey, an endangered duck species, reappeared in the wetlands of Dianchi Lake for the first time in 30 years.

"Although the water deterioration has been halted, the quality is far from satisfactory," said Wu. "We still have a long way to go to protect our mother lake."

In the next two years, Yunnan plans to spend another 7.6 billion yuan (nearly 1.2 billion U.S. dollars) on 64 lake pollution control projects in a bid to make the lake "swimmable" again by 2020.

"Dianchi Lake stretches far into the sky with clear water sparkling in a boundless width. I hope more people could see a crystal clear Dianchi as it used to be," Liu said.