A total of 21 cities have failed to meet the target of improving the quality of black and smelly water bodies, according to the results of an investigation by the nation's environmental regulator.

Among the 739 black and smelly water bodies in 46 cities investigated, the quality of 57 ones has not improved, said Zhang Bo, head of the water environment management division of the Ministry of Ecology and Environment, at a news conference on Thursday.

The 21 cities that failed to meet target include Shanghai, Shenzhen and Guangzhou, and the 25 cities which have met the target include Beijing, Nanjing of Jiangsu province, and Chengdu of Sichuan province.

According to the Water Pollution Prevention and Control Action Plan published in April 2015 and other regulations, major cities in the country should have eliminated 90 percent of the black and smelly water bodies by the end of 2017.

Since May, the Ministry of Ecology and Environment and the Ministry of Housing and Urban-Rural Development have sent 32 investigation groups to 70 cities in 30 provinces to investigate the results of the treatment of black and smelly water bodies.