Pollution of the Yellow River, China's second longest after the Yangtze, is getting worse, with more than 66 percent of the water undrinkable.

The statistics come in the latest annual report on Yellow River water resources.

Only 33.3 percent of the water is category 3 - okay for drinking, aquatic breeding, fisheries or swimming, down from 40 percent in the 1990s, according to the report by the Yellow River Water Resources Committee.

More than 4.35 billion tons of waste water were dumped into the Yellow River in 2005, about 88 million tons more than last year, it said.

More than 73 percent of the waste water was discharged from factories, 298 million tons more than last year.

Apart from pollution, the river is suffering from a dramatic decrease in water flow, mainly due to low rainfall and overuse.

The 5,464-kilometer Yellow River originates in Qinghai Province in the country's northwest and flows through Gansu, Shaanxi, Shanxi and Henan provinces and Ningxia and Inner Mongolia autonomous regions, before emptying into the Bohai Sea.

Known as the cradle of early Chinese civilization, the Yellow River supplies water to more than 155 million people and 15 percent of China's farmland.

In recent years, central and local governments have taken measures to curb pollution, including huge investments in the construction of waste-treatment plants and the forced closure of heavily polluting factories along the river.

Six more automatic water quality monitoring stations will be added to the existing two along the Yellow River by 2010 to help control the pollution.