in Microbes in Human Welfare by

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The sewage water from industries is drained into the rivers and ponds which results in their stagnation. This leads to Eutrophication i.e. excess growth of algae and water hyacinth which leads to oxygen depletion and affects the aquatic life. The sewage increases the Biological Oxygen Demand (BOD) and Chemical Oxygen Demand (COD).

Sewage contains many harmful chemicals such as radioactive substances which affect the aquatic life as well as human life.
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