What is Eutrophication ? 

Explanation

It is the natural aging of a lake by biological enrichment of its water.
Due to addition of nutrients such as nitrogen and phosphorus that encourage the growth of aquatic organism the accumulation of organic remains in course of time leads to shallowing of lake.
Over the centuries the silt and organic debris piles up at the bottom of lake and encourage the growth of marsh plants in the shallow and begin to fill in the original lake basin.
Eventually large masses of floating plants grows and finally converting into land.
The pollutants from man.s activities such as effluents from the industries and homes radically accelerate the aging of lake.
This phenomenon is called Cultural or Accelerated Eutrophication.
Main contaminants include nitrates, phosphates that act as plant nutrients.
They increase the growth of algae, causing unsightly scumand unpleasant odours and depleting the dissolved oxygen of water which is  important for other aquatic life.