(i) Sewage
– Dissolve oxygen in water is used by bacteria and thus most of the living organisms in water die and this water becomes cloudy and smelly.
(ii) Fertilizers
– Rain washes fertilizers into rivers and lakes and thus bacteria grow faster and again use up all oxygen dissolve in water.
(iii) Chemicals / Pesticides
– Acids, alkalis, dyes and spraying chemicals are poisonous to animals and plants.
(iv) Oil forms layers on water and detergents form foam in water and thus no more oxygen dissolved in water from atmosphere.
Kavungya answered the question on March 25, 2019 at 10:30
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