Diff. between eutrophication and algal bloom?

​Both are different but interlinked processes.

Eutrophication refers to the nutrient enrichment in the water bodies leading to lack of oxygen and deadening of life supporting environment. Usually rapid increases in the nutrient status of a body of water happen, by both natural and occurring as a byproduct of human activity. It may be caused by run – off of artificial fertilizers from agricultural land, or by input of sewage or animal waste. This increased nutrient content of the water body causes excess growth of algae. This algal bloom covers the water surface, secrete toxins and reduce oxygen content of water. Oxygen deficiency may cause the death of aquatic animals. 

An algal bloom means the excessive growth planktonic form in the water which is rich in nutrients. .These planktons multiply and reproduce forming a layer on the surface of water. This layer blocks the penetration of sunlight inside the water body . When the light is not able to penetrate inside then the aquatic plants that grow under water are not able to perform the process of photosynthesis which decreases the productivity of the water body and eventually leads to the pollution . The excreta of the planktonic forms accumulate over the surface of water causing a bad odour .