The quality of estuary water in 50 of China's rivers was below grade V in the first half of the year, the State Oceanic Administration (SOA) said Thursday.

China uses a six-grade classification scheme for water quality. Grade I is the best. Water no worse than grade III can be used for drinking, although sometimes treatment is required. Water worse than grade V cannot be used for irrigation.

The SOA tested water quality in 71 estuaries and 427 sewage outflows and found major elements -- including chemical oxygen demand, phosphorus and ammonia -- in excess of the discharge standard in the 50 rivers.

The marine environment information showed that among the 71, Biliu River in northeast China, Jinjiang and Dongxi Rivers in the southeast's Fujian Province, and the Pearl River in Guangdong, met grade II quality standards.

The 50 rivers with quality worse than grade V include the Qiantang River in the eastern province of Zhejiang, Daliao River in northeast China's Liaoning province and Shenzhen River in Guangdong.

Quality of both of China's major rivers, the Yellow and Yangtze, was grade IV.