Inorganic nitrogen and phosphates, found in great quantities in industrial waste water and sewage, remain major threats and may have been the elements that caused red tide to occur in 2000 and 2001. Discharge in coastal waters around Shanghai comes mainly from the Yangtze River. The Yangtze River's drainage area covers an immense area - almost half of China. Over 10 big industrial cities border the river and industrial waste water coming from these cities cause 90% of the direct pollution. Shanghai itself accounts for 10% of the total pollutants. Shanghai is discharging 2.5 million tons of industrial sewage and 3 million tons of human sewage every day into the river. The city has the capacity to treat approximately 500,000 tons of sewage daily, far less than the amount produced. The polluted sea water forms a belt which stretches 4,300 metres and is 500 metres wide just off the Shanghai coast.