Eutrophication is a process of water deterioration, directly related to the saturation of water bodies with various nutrients (Phosphorus, Nitrogen), which leads to an increase in biological productivity.
As mentioned above, the main reason is the intake of excess amounts of phosphorus and nitrogen compounds into the water bodies, which contribute to the further growth of other biological organisms that inhabit the water bodies.
This phenomenon is absolutely natural, but the contribution of anthropogenic factors is also included, for example, an increase in emissions of various household and agricultural wastes in sewage, rivers, etc.
rapid growth of vegetation in a pond;
subsequent growth of zooplankton;
the amount of oxygen entering the water decreases, which contributes to the death of aerobic organisms and the reproduction of anaerobic;
leads to the "flowering" of water, etc.