On weekends and holidays, many residents of Maoming and nearby areas drive to Haoxin (literally good-hearted) Lake, to enjoy the cool breeze, ride bicycles, walk dogs, have picnics or fly kites.

Surrounded by shady trees and blooming flowers all year long and shimmering like a sapphire under the sunlight, Haoxin Lake appears much like many other renowned lakes at home and abroad.

So it might surprise you to learn that the lake is actually manmade. In fact, until 2013, its site had served as an open-pit mine which covered a mammoth area of 6 square kilometers and 90 meters at its deepest point, and had all kinds of waste.

The open-pit mine dates back to the 1950s when China urgently needed energy and discovered oil shale there by accident.

The oil shale reserve was estimated at 5 billion tons against the nation's oil refining capacity of less than 500,000 tons at that time.

The Chinese government then decided to exploit the oil shale and refine oil there, turning Maoming into the Southern Oil City.

The oil refinery opened in early 1962 and, during its operation, extracted 102 million tons of total oil shale, yielding 2.91 million tons of crude oil. The mine closed down in 1993 for a number of reasons, including environmental pollution and the high costs associated with exploitation, according to local historical documents.

The mine later became a furtive dumpsite for many irresponsible enterprises, worsening the surrounding environment.

In 2013, the Maoming government decided to treat this "city scar" as part of its efforts to improve the city's environment.

"It was by no means an easy decision for the Maoming authorities to make," noted Li Hualin, an official who was involved in the project transformation.

For one, the site has rich reserves of kaolin clay, coal and iron ore in addition to oil shale, which meant a huge bonanza for a city with less wealth than those of the Pearl River Delta region, he explained.

For another, transforming the mine into a lake would require much money.

"Nevertheless, the idea of prioritizing the environment prevailed at last," he said.

Li said that the lake was named Haoxin Lake, to commemorate the ancient local heroine Madame Xian, who was highly honored by the emperors of three dynasties for her kindheartedness and outstanding leadership in the sixth century, and to promote the benevolent tradition of the Maoming people.

According to Li, 160 million cubic meters of freshwater was channeled from the Gaozhou Reservoir nearby to the mine and about 400,000 trees were planted all around an area of over 533 hectares.

Apart from environmental restoration, Maoming also developed cultural facilities in the area, where abandoned factories became a museum and a road of 40 kilometers was constructed.

A former shale oil development in Maoming, Guangdong province, has been transformed into a natural park. [Photo provided to chinadaily.com.cn]