During an educational trip, a student of botany saw a beautiful lake in a village. She collected many plants from that area. She notices that villagers were washings clothes around the lake and at some places waste material from houses was destroying its beauty.
After few years, shw visited the same lake again. She was suprised to find that the lake was covered with algae, stinking smell was coming out and its water had become unusable. Can you explain the reason for this condition of the lake ?

Explanation

This is explained with the help of process known as Eutrophication. Waste materials and detergents used in washing of clothes contain lot of phosphates in them. The presence of these phosphates in water increases growth of algae. This convers the surface of water in a lake and as a result, oxygen content of water decreases. This leads to anaerobic condiltions resulting in the death of animals and also inhibits the growth of other water animals. Since oxygen is very essential for animal life, in its absence, there is decay and death of animals leading to stinking and foul smell.