TAIYUAN -- Sixty-nine-year-old Duan Zhu in North China's Shanxi province has kept the hobby of winter swimming for over two decades as he believes an icy dip is good for his physical health. Still, it was not always easy for him to find a river clean enough to swim in until the recent decade.

Duan lives near Fenhe River in Taiyuan, the capital of coal-rich Shanxi. "I usually swam in small ponds near Fenhe River as the water was clearer and safer," said Duan.

As the second-largest tributary of the Yellow River, the river stretches over 710 kilometers, feeding a quarter of the population of Shanxi, thus known as the "mother river" of Shanxi.

But since the 1970s, the groundwater level in the Fenhe River basin has dropped significantly, and the water quality in the mainstream has deteriorated due to pollution.

Changes and water treatment efforts along the river began in 1998, and today, the Taiyuan section of the river has become a popular tourist site, attracting swimmers like Duan and visitors.

Zhang Yuhong, 49, a local in Taiyuan, participated in the pollution treatment.

"To improve the flood control capacity, the first phase of the project started with reinforcing and expanding the embankment," said Zhang.

He recalled that the watercourse was overgrown with weeds then, and over 1,000 residents volunteered to remove the weeds to expand the water storage.

In August 2000, the river's Taiyuan section began to retain water, and residents swarmed onto the river bank to cheer for it.

Ecological restoration of the Taiyuan section was completed in Autumn 2021, after more than two decades of efforts in pollution control, sludge dredging, water diversion, and greening of the banks.

"These efforts have been very helpful to flood control, solving urban waterlogging, and increasing air humidity," said Zhang, now in charge of flood control of the scenic spot of Fenhe's Taiyuan section.

Taiyuan pioneered the overall treatment of the Fenhe River.

Linfen, which sits along the river, was previously known as a heavily polluted city. The local government shut down many seriously polluting enterprises and made efforts to restore the river channels.

In addition to environmental and social benefits, the cleanup also brought economic benefits.

In Quwo county, administered by Linfen, mushrooms and flowers are harvested on farmland covering 2,500 mu (about 166.7 hectares). Before treatment, it was saline land. The farmland is now the city's largest seedling nursery base.

"The annual profit is about 35 million yuan (about $4.8 million), and local farmers also profit from it by renting their farmland to and working in the company," said Yang Xu, general manager of the company which runs the farmland.

In recent years, Shanxi has rolled out a series of rules and regulations to accelerate the treatment and protection of rivers and lakes. Many wetland parks were set up along rivers, benefiting millions of people.