China's National Audit Office (NAO) said Friday that 18 sewage treatment plants failed to meet water quality and discharge standards during an inspection of water pollution control in the Bohai Sea.

The NAO team inspected 51 sewage treatment plants operating in 13 large and medium-sized cities around the Bohai Sea, including Tianjin, Dalian, Qinhuangdao and Yantai, said a statement posted on the NAO website Friday.

The inspection lasted from March to September last year.

Meanwhile, 41 of the 180 enterprises under state-level monitoring had exceeded discharge requirements for waste water, said the statement.

The statement said 35 of the 41 polluting enterprises belonged to highly-polluting industries, including the petrochemical, paper-making, printing and dyeing sectors.

The statement also said the task of ensuring industrial and domestic waste water treatment remained arduous, and thorough monitoring of smaller companies was difficult.

Huang Daoguo, head of the NAO's department of agriculture, resources and environmental protection, said local governments still had great room to stringently implement water treatment measures and improve water treatment capacity.

The NAO ordered local governments to step up water pollution control efforts, close highly-polluting outdated production capacity, build more treatment plants and improve those plants failing to meet standards.

The rim of the Bohai Sea covers Shandong, Hebei and Liaoning provinces, and the port city of Tianjin. The Bohai Sea covers about 77,000 square kilometers.

The statement gave no details of water quality in the Bohai Sea.

A report released on May 8 by the State Oceanic Administration showed the Bohai Sea water quality in summer was better than in autumn in 2008, without specifying reasons.

About 13,810 square kilometers of sea area was polluted last summer, accounting for 17.9 percent of the total, and 23,680 square kilometers was polluted in autumn, accounting for 30.8 percent of the total area.

Of the three bays in the Bohai Sea -- Laizhou Bay, Liaodong Bay and Bohai Bay -- Laizhou was most polluted, while Liaodong was least polluted, according to the administration.

Laizhou Bay borders Shandong Province, while Liaodong Bay neighbors Liaoning Province.

(Xinhua News Agency May 22, 2009)