Sometimes the presence of water blooms in the mill shows:

Sometimes the presence of water blooms in the mill shows: Correct Answer Oxygen deficiency

Key Points

Water Blooms or Algal blooms:

• Algal bloom is a rapid increase or accumulation in the population of algae in an aquatic system. 
• Algal blooms may occur in freshwater as well as marine environments. 
• Most algal blooms are not harmful but some produce toxins and do affect fish, birds, marine mammals and humans. 
• The toxins may also make the surrounding air difficult to breathe. 
• These are known as Harmful Algal Blooms (HABs).  
• HABs limit the penetration of light causing die-offs of plants in littoral zones and their dependent population. 
• To decompose these dead organisms, a large quantity of Oxygen is consumed. 
• This increases the Biological Oxygen Demand (BOD) of water. 
• Dissolved oxygen decreases and results in fishkills. 
• In worst cases, it leads to Hypoxia of water bodies, further leading to the formation of dead zones where water can no longer support life.  
• The colour of the water changes and it also gives a foul, obnoxious smell making the water unfit for drinking purposes.  

Hence, the presence of water blooms is due to oxygen deficiency.