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

The process of eutrophication is responsible for this condition of lake. The domestic waste and organic compounds such as detergents can provides plant nutrients which can enhance the growth for alager and aquatic plants.
These are decomposed by the bacterial population giving disagreeable odour and spoilling the beauty of the lake.