What are algal blooms? How are they formed? Give the harmful effects of formation of algal blooms in an aquatic body.

Explanation

Domestic sewage contains nutrients like nitrogen and phosphorus which favours the excessive growth of algae (free floating) called algal bloom.
The harmful effects:
(i) Deterioration of water quality and imbalance of water ecosystem.
(ii) Fish mortality rate increases.
(iii) Some bloom forming algae are extremely toxic to human beings and animals.