<P> There have been a high number of river pollution incidents in recent years in China, such as drinking water source pollution by algae in the Lake Tai, Wuxi in May 2007 . There was a "bloom of blue - green algae that gave off a rotten smell" shutting off the main source of drinking water supply to 5.8 million people . By September 2007, the city had closed or given notice to close more than 1,340 polluting factories . The city ordered the rest to clean up by June or be permanently shut down . The closing of the factories resulted in a 15% reduction of local GDP . The severe pollution had been known for many years, but factories had been allowed to continue to operate until the crisis erupted . </P> <P> The 2005 Jilin chemical plant explosions in Jilin City caused a large discharge of nitrobenzene into the Songhua River . Levels of the carcinogen were so high that the entire water supply to Harbin city (pop 3.8 M) was cut off for five days between November 21, 2005 and November 26, 2005, though it was only on November 23 that officials admitted that a severe pollution incident was the reason for the cutoff . </P> <P> Chinese environmental activist and journalist Ma Jun warned in 2006 that China is facing a water crisis that includes water shortages, water pollution and a deterioration in water quality . Ma argued that 400 out of 600 cities in China are facing water shortages to varying degrees, including 30 out of the 32 largest cities . Furthermore, Ma argued, discharges of waste water have increased continually over the years 2001 - 2006, and that 300 million peasants' drinking water is not safe . He warned: "In the north, due to the drying up of the surface water, the underground water has been over-extracted . The water shortage in the north could have drastic affects because almost half of China's population lives on only 15 percent of its water . The situation is not sustainable . Though the south has abundant water, there is a lack of clean water due to serious water pollution . Even water - abundant deltas like the Yangtze and the Pearl River suffer from water shortages ." </P> <P> According to an article in the Guardian, in 2005, deputy minister Qiu Baoxing stated that more than 100 out of the 660 cities had extreme water shortages . Pan Yue, deputy director of the state environment protection agency, warned that economic growth was unsustainable due to the water problems . In 2004 the World Bank warned that the scarcity of the resource would lead to "a fight between rural interests, urban interests and industrial interests on who gets water in China ." In April 2005 there were dozens of injuries in Dongyang city, Zhejiang Province, due to clashes over the nearby chemical factories of the Juxi Industrial Park accused of water pollution that harmed crops and led to deformed babies being born . According to the article, a quarter of the population lacked clean drinking water and less than a third of the waste was treated . China is expected to face worsening water shortages until 2030 when the population peaks . </P>

Of 600 large cities in china about how many are experiencing a water shortage