(N/A) Water pollution is caused by the addition of:
$(i)$ Undesirable substances like fertilizers,pesticides,or other poisonous chemicals.
$(ii)$ Sewage directly entering a water body.
$(iii)$ Hot water from power plants,which increases the water temperature and reduces dissolved oxygen,thereby killing aquatic organisms.
$(iv)$ Industrial effluents or radioactive substances discharged into water bodies.
We can contribute to reducing water pollution by taking the following measures:
$(i)$ Sewer lines should not be directly connected to water bodies.
$(ii)$ We should not dispose of garbage or domestic waste into water bodies.
$(iii)$ Prevent the dumping of toxic compounds into water bodies.
$(iv)$ Avoid washing clothes near water bodies,as detergents contain harmful chemicals.
$(v)$ Plant trees near river banks to prevent soil erosion,as erosion leads to the siltation of water bodies.