Objective   To assess the eutrophication and discuss the relationship between the pollution of alga and microcystins and digestive system cancers.

  Methods   The data from the typical surveillance and the published research papers are packed up and re-analyzed.The drinking water's physical and chemical index were sampled and determined according to GB5750.The sample and determination of alga and chlorophyll were conducted according to "regulation for investigation on eutrophication of lakes".Microcystins were determined with ELISA method.

  Results   Categories of algae were mainly cyanophyta, cryptophyta, euglenophyta, chlorophyta.The grade of eutrophication can be classified successively as the most eutrophic, Luoma lake, Beishan Water-reservoir, river freshwater in Rudong and Canal, mesotrophic, and Yangtse river the oligotrophic.The descending ranking of microcystins positive rate was ditch-pool water, river water, shallow-well water, while that of deep-well water was zero.The water out of water plants whose source water were Tai lake contained microcystins.The highest death rate of liver cancer was found in the habitants who drank and used the house ditch water, and then pool water, river water, the lowest was shallow-well water.Popular regions of alimentary canal tumors were mainly ones where source water were eutrophicated and had comparatively high mycrocystins.

  Conclusion   The pollution of alga and alga toxins became the important factor of universally aggravating source water.The eutrophication and pollution of alga and microcystins did harm to human's health, which clearly indicated the relation between alga, microcystins and high popularity of tumors.