BEIJING — China's air and water quality improved from January to April, according to a report issued by China's Ministry of Ecology and Environment.

The report showed that 81.2 percent of surface water quality was graded Class I to III (good water quality) in the first four months, up 6.2 percentage points from the same period last year, while that of Class V fell by 4.1 percentage points year-on-year to 1.4 percent.

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

For major rivers, including the Yangtze River and the Yellow River, 84.5 percent of the water quality was graded Class I to III, up 7.2 percentage points year-on-year, and 1.2 percent was graded as Class V, down 4.9 percentage points year-on-year.

The percentage of days with good air quality was 84.8 percent in 337 cities at and above the prefecture-level in January-April, up 5 percentage points year-on-year. The average concentration of PM2.5 (atmospheric particulate matter) was 42 micrograms per cubic meter in January-April, down 12.5 percent year-on-year.

Among the cities, Haikou in Hainan province, Lhasa in the Tibet autonomous region and Lishui in Zhejiang province ranked as the top three for good air quality in the first four months.