______ kills the fish by deoxygenating water. Which among them doesn’t fits in the blank.

The correct answer is Dust in the air.

Key Points

• Sewage dumped in the river contaminates water which in turn makes it difficult for fish to survive.
  • Alternatively, when the sewage is released into rivers, it contains a lot of nitrogen and phosphorous. 
  • These can stimulate the growth of algae, such as phytoplankton in the water or mats known as biofilms in the sediments, which can lead to algal blooms.
  • These algal blooms decrease the concentration of oxygen and fish die.
• Eutrophication
  • It refers to the accumulation of nutrients such as phosphates and nitrates in water bodies over time which stimulates the growth of algae.
  • It results in the reduction of dissolved oxygen.
• BOD means Biological Oxygen Demand
  • Biochemical oxygen demand is the amount of oxygen consumed by bacteria and other microorganisms while they decompose organic matter under aerobic conditions.
  • Dissolved oxygen is a crucial component of natural water bodies, maintaining aquatic life.
  • However, increased BOD means that the bacteria are consuming more available oxygen and hence, available oxygen is less for fish.
  • High biochemical oxygen demand can be caused by: high levels of organic pollution, caused usually by poorly treated wastewater; high nitrate levels, which trigger high plant growth.