BEIJING, July 30 (Xinhua) -- China's water quality nationwide improved slightly in 2008 though the situation was still grave, said a statement released by the Ministry of Environmental Protection on Thursday.

    The quality of the water sampled in 55 percent of 409 monitoring stations set up along 200 rivers, including the Yangtze and the Yellow rivers, fell nto levels I to III last year, up from 49.9 percent in 2007, the statement said.

    China classifies water quality in major rivers and lakes into six levels, ranging from level I, which is good for drinking, to level VI, which is too polluted for any purpose.

    Levels I to III means water quality is okay for drinking, aquatic breeding, fisheries and swimming.

    According to the document, 24.2 percent of the samples fell into levels IV and V, okay for industrial use and farm irrigation, down from 26.5 percent in 2007.

    And 20.8 percent of the samples were ranked level VI, down from 23.6 percent in 2007.

    In addition, pollution was reduced slightly in 28 major lakes and reservoirs under state surveillance. Four of them met level II, up from two in 2005. However, 11 lakes and reservoirs were still categorized level VI while the figure was 12 in 2005.

    The ministry attributed the progress to increasing investment in pollution control and tougher penalties for polluters.

    The government invested 5 billion yuan (731.92 million U.S. dollars) in 2007 and 2008 to clean up four major rivers and three lakes, the statement said.

    It also spent 6.5 billion yuan in 2007 and 7 billion yuan in 2008 in building sewage treatment plants in cities, counties and some townships.

    From 2004 to 2008, the environment authorities investigated and punished 120,000 enterprises that violated environment laws.

    The figure in 2008 was 15,000. According to another report on the ministry's website, the figure in 2007 was about 17,000.

    In the five years, they also closed more than 20,000 polluters. In 2008, 845 polluting projects near sources of drinking water were closed as were 621 paper mills that failed to meet state environment standards. The document did not reveal the figure for 2007.