Answer:
Algal Bloom causes depletion of oxygen level due to eutrophication in the river water.
Explanation:
An algal bloom is a fast increase in the growth of algae due to the presence of excessive nutrients particularly Phosphorus and nitrogen due to water contamination from sewage water.
As the population of algae increases, it depletes the oxygen in the water and this process is known as eutrophication, which affects the living organisms of the river. In certain cases, these algal Bloom also produces toxins and causes harm to other organisms.
