It is the process of depletion of oxygen from water bodies occurring either naturally or due to . human activities. The process of eutrophication takes place due to introduction of nutrients and chemicals through discharge of domestic sewage, industrial effluents and fertilizers from agricultural field. Algae and phytoplankton use carbon dioxide, inorganic nitrogen and phosphate from the water as food. This cause death of most of the aquatic organisms, draining water of all its oxygen.