BEIJING — China's water quality improved in the first five months of the year, according to data released by China's Ministry of Ecology and Environment.

The data shows that 81.8 percent of surface water was graded Class I to III (good quality) in the January-May period, up 1 percentage point from the same period last year, while the figure for Class V water fell 0.7 percentage points year on year to 2.1 percent.

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

For major rivers, including the Yangtze River and the Yellow River, 83.5 percent of the water quality was graded Class I to III in the first five months, up 1.2 percentage points year-on-year, and 2 percent was graded Class V, down 0.8 percentage points year-on-year.