The Yangtze River has become the major source of pollution for the coastal area of east China's Zhejiang Province, a survey shows.

Zhejiang's coastal area receives one third of the total runoff of the Yangtze, and the pollution caused by it has far exceeded that of the rivers in Zhejiang, according to a survey conducted by the National Bureau of Oceanography.

The 6,300-km-long Yangtze, China's longest river, carries a significant amount of pollutants into the sea as it flows through many industrial cities including Shanghai, the survey says.

This also caused frequent occurrences of red tides in the East China Sea. According to statistics, China had 265 red tides from 1993 to 1997, half of which occurred in the East China Sea.

Eight rivers in the province, including the Qiantang River, also release pollutants into its coastal areas, according to the survey.