The uncontrolled growth of algae and their subsequent descent into the depths of the body of water stimulates an active benthic community (bacteria), which depletes oxygen levels due to respiration. The algae may also cover the surface of the water, reducing the amount of light that penetrates into the photic zone, decreasing photosynthesis in aquatic autotrophs. The decreased level of dissolved oxygen can result in the death of any number of larger communities.
See related links below for more information about eutrophication and the effect it has on the ecosystem.
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