Zuo Lihua, 80, recalled the grim conditions of polluted lakefronts in the coastal city of Xiamen, Fujian province, four decades ago, when chickens, ducks and pigs freely roamed crowded streets.

In the early 1980s, Yundang Lake was one of the worst — a body of water spoiled by sewage, garbage and pest infestations. The putrid conditions were in stark contrast to the vibrant community that now flourishes around the lake's rejuvenated environment.

The lake, once part of bustling Yundang Port, has since been cleaned up to become a thriving urban haven thanks to a succession of measures taken by researchers and local authorities.

Nowadays, Zuo, a retired nurse, regularly goes for hourlong walks in a park near the lake. She also takes advantage of a newly built fitness trail and enjoys looking at egrets that hover around the body of water.

In the 1970s, a crucial change happened with the construction of a western embankment, transforming Yundang Port into a sprawling lake, according to the Ministry of Natural Resources. The port, which was connected to the sea, covered 10 square kilometers while the area of Yundang Lake was 2.2 square kilometers.

However, in the early 1980s rapid economic development brought industrial pollution and fish and shrimp disappeared from the lake. Back then, more than 100 polluting enterprises, including paper mills, tanneries, breweries, and electroplating factories, discharged wastewater into Yundang.

Xi leads action

A meeting chaired by Xi Jinping, then serving as executive vice mayor of Xiamen, in 1988 set in motion a comprehensive strategy to revitalize the lake.

The meeting outlined a plan that detailed legal governance, stopping pollution, dredging work, revitalization of the body of water and improvement of the surrounding environment.

In the same year, the Standing Committee of the People's Congress of Xiamen passed the "Accelerating the Comprehensive Improvement of Yundang Lake" proposal, which outlined the principles for restoration work.

At that time, 45 percent of the city's industrial wastewater and half of Xiamen's domestic sewage was discharged into the lake. Cutting off sources of pollution and treating sewage were crucial steps to improving the water quality, according to the local government. The Xiamen government eventually shut down or relocated major polluting industrial plants.

Supervision of Xiamen's drainage system was also stepped up and a major innovation was introduced.

Wang Yanyan, chief engineer of Xiamen's Municipal Affairs and Gardens Bureau, said they now manage the city's drainage system for both residential and business areas.

The bureau regularly inspects and supervises renovations and new construction in business areas to ensure polluting waste doesn't make its way into the waterways. "We instruct business owners to install the necessary infrastructure, including grease traps, and to also obtain drainage permits before they renovate business premises," she said.

The preventive approach aims to stop grease and waste from blocking drainage systems. There are also two drainage systems that separate rainwater from wastewater. The wastewater is then treated before being discharged into rivers and lakes, she said.

"The drainage management authority tracks and manages the system. It's like a doctor regularly tracking (the system's) health and taking care of it," Wang said.

The Xiamen government has also used tidal differentials to connect the lake to the sea, facilitating water exchanges during low and high tides. This movement of water has transformed the once stagnant lake into a dynamic and thriving ecosystem and promoted a healthier aquatic environment.