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.

Sea dikes removed

In the 1920s, Xiamen began expanding its area by reclaiming land from the East Sea through the building of dikes.

Back then, travel from Xiamen Island relied heavily on shipping. Sea dikes not only guarded against waves, but also enabled rail lines and highways to be built to better connect the city to outside areas and boost economic growth.

The sea dikes, including one near Yundang Port, enhanced industries such as salt fields and aquaculture. However, the dikes also created a pollution problem.

Pan Shijian, former vice chairman of the Xiamen Committee of the Chinese People's Political Consultative Conference, said: "Xiamen experiences two influxes of seawater from the Taiwan Strait, bringing clean seawater into the city. If we were to fill in the bay and turn it into land, our tidal inflow would greatly decrease, leading to a dismal future for this city.

"Despite the large cost and efforts, the Xiamen government made a resolute decision to open up the sea walls and clear millions of cubic meters of sediment, introducing seawater into bays."

Xiamen removed all the dikes that it could. Those needed for flood management and tide control were kept, and sluice gates or additional openings were added. Since 1988, Xiamen has opened seven sea dikes, including ones at Yundang Lake and Maluan Bay, the Ministry of Natural Resources said.

With the completion of sea-crossing bridges and tunnels such as the Xiamen Bridge, Haicang Bridge and Xiang'an Tunnel, the transportation functions once shouldered by the sea dikes have gradually diminished. The sea dikes had curbed Xiamen's efforts to improve the environment and achieve high-quality urban development, the ministry said.

"Returning much of the land to the sea is something you may find hard to imagine. It required a significant amount of money and it seemed unbelievable at the time," Pan said.

Mangroves restored

So far, the renovation of Yundang Lake has cost about 1.99 billion yuan ($277 million).

"We are not only engaged in environmental restoration, but also preserving our city's culture," Pan said.

"For example, our sailing sports lead the way in China. People in Xiamen no longer just observe the sea from the shore. They can now sail and see dolphins in the sea. It has changed our lifestyle."

To restore wetlands, the city's forestry bureau and Xiamen University planted mangroves along lakefronts and seashores.

The mangrove restoration projects were done in "forest-friendly" areas including Yundang Lake and Tong'an Bay. The area of mangrove forests in Xiamen increased from around 33 hectares in 2000 to 174 hectares in 2023, the ministry said.

As mangrove plantations expanded, marine ecosystems flourished, with water birds returning to nest and frolic.

In the past, coastal waters in Xiamen suffered from severe eutrophication — an overabundance of nutrients such as nitrogen and phosphorus in water caused by excessive aquaculture and haphazard development.

As a result, the native mangrove forests, known for their crucial role in protecting coastlines and mitigating the impact of waves, disappeared.

Yang Shengchang, an associate professor of environmental studies at Xiamen University, said: "Replanting mangroves by the sea posed challenges. The elevation of the plant above mud flats had to be carefully considered to avoid long submersion that could hinder sapling growth.

"Selecting suitable species required extensive experimentation to ensure adaptability to the local environment. Moreover, the planting density had to be the best to withstand tidal forces without being washed away."

'Chopstick' technology

To address these challenges, researchers at Xiamen University developed a patented chopstick seedling technology.

"A seedling without enough height has difficulty surviving. We use a chopstick to raise the height of the seedling so its survival rate has become higher," Yang said.

The research team conducts regular monitoring to ensure the growth of the plant.

These efforts have revived the once-dwindling mangrove areas and increased protection of vital coastal ecosystems, providing a sanctuary for thousands of egrets during the nesting season.

Chinese modernization aims for harmonious coexistence between people and nature. Respecting nature, and conforming to and protecting it are requirements of this belief, the ministry said while commenting on the environmental protection practices in place in Xiamen.

Luo Ming, director of the Ministry of Natural Resources' Key Laboratory of Consolidation and Rehabilitation, said Xiamen adopted nature-based solutions to mitigate environmental damage at every stage of the restoration project, be it planning, design or implementation.

"With more people and less land, Xiamen's water resources are scarce, so sustainable development is extremely critical," she said. "Habitat loss resulting from extensive urban development, such as the filling of lakes in Xiamen, used to be a challenge."

Global ecosystem restoration standards focus on eliminating threats, establishing local ecosystems and reconnecting restored ecosystems with their external environments, she said, adding that's how Xiamen achieved its goals.

The effectiveness of this approach relies on enhancing urban resilience in the face of climate change, promoting "sponge land" for sustainable water management and protecting biodiversity by restoring natural habitats for species like migratory egrets.

Xiamen also managed to achieve its environmental protection targets without sacrificing economic growth. The city only accounts for 1.4 percent of Fujian's land area, but in 2022 it accounted for 14.7 percent of the province's GDP, up from 13.2 percent in 2000. Nearly half of the province's import and export value was from the city, and the per capita disposable annual income in Xiamen was about 68,000 yuan in 2022.

Meanwhile, the water quality compliance rate of major river basins has been maintained at 100 percent for many years, the local government said.