How is life of organisms living in water affected when water gets polluted?

Water gets polluted from domestic wastes (loaded with detergents, faecal matter, etc.), fertilisers and pesticides
from crop fields and industrial wastes (heavy metals, waste heat).
(i) Fertilisers and domestic wastes cause eutrophication or increased organic loading and excessive growth of algae (algal bloom). This ultimately reduces oxygen available to aquatic animals (fish, molluscs) and kill them.
(ii) Domestic wastes also carry pathogens of a number of human diseases. Some of them can cause diseases of animals as well.
(iii) Pesticides and pollutants of industrial wastes directly harm the aquatic organisms and humans.