How do algal blooms affect the life in water bodies?

Algal blooms are caused due to excessive growth of planktonic algae on the surface of water. This excessive growth imparts a distinct colour and fowl smell to the water body. The algae causes deterioration of the quality of water in the water body by releasing various toxins and decreasing the oxygen content which results in death of fishes and other water life and may even be sometimes harmful to human beings.