Eutrophication

• An excessive growth or 'blooms' of algae in lakes rich in nutrients such as phosphates is called eutrophication.
• Normally it takes thousands of years to progress, but human activities have enhanced this process greatly.

Eutrophication in a lake

• Human beings add excessive amounts of plant nutrients (primarily phosphorus, nitrogen, and carbon) to streams and lakes in various ways.
• Runoff from agricultural fields and urban lawns, and untreated domestic sewage discharged into lakes are major sources of these nutrients.
• These algal blooms lead to oxygen depletion, as a result of which many fish, birds, and other animals die. Thus, the water begins to stink.