a) Effluent from industries: Waste materials from industries containing enormous
quantities of chemicals are released into the nearby source of water like ponds, lakes,
rivers. Most Indian rivers are polluted by industrial effluents.
b) Accumulation of sewage: Sewage containing vegetable wastes, fruit wastes, animal
excreta, human excreta and organic wastes from factories are released into water
sources.
c) Addition of detergents: Domestic wastes contain a high percentage of detergents.
Detergents on reaching water bodies, they cause foaming and reduction in the
dissolved oxygen content.
d) Addition of agricultural wastes: A variety of pesticides and fertilizers used in agriculture
which are non-biodegradable are washed away into water sources.