BEIJING - China's overall environmental situation is still grave while its seven major rivers and coastal seawaters are slightly polluted, according to an annual report on the country's environmental conditions in 2010 released Friday.

Pollution of surface water continues to be a serious problem, said the report, released by the Ministry of Environmental Protection.

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The overall water quality of the Yangtze and Pearl rivers was fairly good, but that of the five other major rivers was not so healthy, it said.

In 2010, the Songhua River in northeast China and Huaihe River in the east were slightly polluted, while pollution was moderate in the Yellow River in the north and the Liaohe River in the northeast, and heavy in the Haihe River in the north.

Many of the country's lakes and reservoirs were polluted, the report said, adding that 42.3 percent of the 26 lakes and reservoirs under monitoring were eutrophicated.

The report said water quality of the coastal seawaters in the Bohai Sea was bad while that in the East China Sea was extremely bad.

It added that the ratio of the coastal seawaters in good quality decreased in the Bohai Bay, the Yangtze River Estuary and the Pearl River Estuary last year, compared to 2009.

The overall air quality in urban areas across China was good but in some cities the air pollution was still heavy, according to the report.

Of the 471 cities of county-level and above which are under monitoring, 3.6 percent had excellent air quality, while 79.2 percent had fairly good air quality, the report said.

The air in 15.5 percent of the cities was slightly polluted and the air quality was poor or hazardous for the remaining 1.7 percent, it added.

The report said acid rain was observed in 50.4 percent of the country's 494 cities under monitoring and acid rain had an annual average pH of 5.0 or less in 21.6 percent or 107 cities.

Further, the report said no obvious changes were observed in the levels of ionization radiation and electromagnetic radiation in the environment around the country's nuclear facilities.