Inorganic phosphorous and nitrogen are responsible for the growth of algae. In polluted water, it increases due to which algae increases greatly at the surface of water or pond. Extensive increase of these algae is called water bloom. Due to death of these algae their organic matter get decomposed due to which oxygen gets depleted and the aquatic animals die. If these activities persist for long time, the pond have more organic matter and less water. This process is called eutrophication.