The occurrence of red tide is a natural phenomenon. It has a historical record of 1,000 years. 70 of the 300 types of flagellate algae that cause red tide can produce toxin. The toxic red tide is the mainstream of the present red tide disasters.

In May 2000, in the ocean near Zhoushan in Zhejiang Province, red tide stretched over 80 kilometers in an area of 7,000 square kilometers, the largest since 1990s.

The red tide is caused by the land-origin water pollution. For instance, along Yangtze River, the industrial wastewater and sewage emissions are 75 percent and 25 percent respectively. Of the 18 provinces, municipalities and autonomous regions involved, Sichuan, Hubei, Hunan, Jiangsu and Jiangxi provinces and Shanghai are the main wastewater and sewage producers and discharge 84.6 percent of the total pollutant in the river valley...

The water pollution broke the latest line of defense.