How is an algal bloom formed in a water body? Explain the affect it has on the water body.

An algal bloom is a phenomenon of excessive growth of planktonic forms in a nutrient rich water body. As the planktonic species multiply on the surface they form a layer that covers the entire surface of the water body.

Algal bloom affects the quality of the water body in many ways: algal bloom blocks sunlight, which does not reach submerged aquatic plants that may have a role in supplying necessary nutrients to other aquatic life forms and keeping the water clean.

Excretory substances related by planktons build up in concentration and pollute water.

some algae even releases substances that are toxic for other life forms in the water body.

also, Biological oxygen demand (BOD) of the water decreases, due to huge concentration of biomass on the surface., causing many life forms to die. Their carcasses further contribute to the deterioration of the water quality.