Nutrient enrichment of waterbodies due to agricultural run-off which leads to shallowing of waterbodies is known as eutrophication. It is an excessive growth or blooms of algae in lakes rich in nutrients. Normally it takes thousands of years to progress, but human activities have enhanced this process greatly. Human add excessive amount of plant nutrients to streams and lakes.

Eutrophication can be a natural process in lakes, occurring as they age through geological time.

 Untreated domestic sewage discharged into lakes is the major source of these nutrients. These nutrients speed up the algal blooms which, in turn lead to oxygen depletion. As  a result of this, many fish, birds, and other animals die and the water begins to stink.