The Chinese capital is to invest 12.46 billion yuan (US$1.59 billion) between 2006 and 2010 to curb worsening water pollution, according to a plan issued on Wednesday.

The move aims to guarantee a cleaner water supply for the city of 16 million, ahead of the 2008 Summer Olympics.

By then, 90 percent of waste water in urban Beijing and 50 percent in its suburbs will be treated before it flows into rivers and lakes, according to the plan.

The city will block more than 1,000 sewer pipes along 30 of its rivers by 2008.

Beijing will be able to treat all sewage and garbage from 41 villages in an area of 362 square kilometers near Miyun, Huairou, and Guanting reservoirs, the city's major drinking water sources, the same year.

Under the plan, the city will tackle soil erosion over 3,560 square kilometers near or upstream from Miyun and Guanting reservoirs by 2010.

The environmental protection bureau says untreated waste water, industrial effluent and agricultural pollution are responsible for the deteriorating water quality of its rivers, reservoirs and lakes.

The bureau said earlier this week that pollution of Beijing's water supply was getting worse, and water from the Guanting reservoir, the city's fourth largest source of drinking water, was not fit for human consumption or even irrigation.

At level five on the water pollution index, water is only suitable for irrigation. At below level five, water from the Guanting reservoir is not fit for growing agricultural produce.

With 21 reservoirs, Beijing faced grave water supply problems as the Zhaitang, Taoyukou, Niantan and Daning reservoirs had all dried up, said the bureau in its first monthly report on water quality.

Miyun, Huairou and Yanqinggucheng reservoirs, the capital's other major drinking water sources, are still providing clean, potable water, said the report which is posted on the bureau's website.

Water quality levels between one and three are considered potable.

The report also said nearly half of Beijing's scenic lakes and ponds were polluted and their water was unfit to irrigate the park landscape around them.

The report said water quality in seven of Beijing lakes, such as the Winter Palace Lake and Taoranting Lake, was below level five. Only four lakes could be used to supply drinking water, while water from the other lakes was only fit for industrial use.