XI'AN, Oct. 13 (Xinhua) -- The Weihe River, the longest tributary of the Yellow River once haunted by pollution, saw improved water quality in recent years, according to the Shaanxi provincial department of ecology and environment.

Official data showed that 73 percent of surface water at monitoring points in the Shaanxi section of the Weihe River was graded Class I to III (good quality) last year, up 4.7 percentage points from 2018. In the first half of this year, the figure rose to 77.8 percent.

Surface water quality is divided into five classes in China, with Class I being the best.

The 818-km Weihe River originates in Gansu Province and flows past major cities in Shaanxi, including Baoji, Xianyang, Xi'an and Weinan.

The river has been seriously polluted since the 1980s, as a result of waste discharged from paper mills and other high-polluting plants.

Wang Qing, an official with the department, said Shaanxi has launched 25 relevant laws and regulations to provide a legal basis and policy guarantee for the protection of the Weihe River.

Over the past five years, Shaanxi has closed 33 polluting enterprises in the Weihe River basin. A total of 70 sewage treatment plants have been set up and put into use in surrounding cities and counties.