Question

A river with an inflow of domestic sewage rich in organic
waste may result in

• A. Increased population of aquatic food web organisms
  
• B. Drying of the river very soon due to algal bloom
• C. An increased production of fish due to biodegradable nutrients
• D. Death of fish due to lack of oxygen

Answer 1

The correct option is D Death of fish due to lack of oxygen

Effect of sewage influx into the river

Sewage is rich in organic matter.

Increased organic matter will lead to the growth of aerobic bacteria that decompose the organic matter using the dissolved oxygen in the lake.

Therefore the level of dissolved oxygen in the lake will be reduced.

Lower level of dissolved oxygen (DO) would cause the death of aquatic animals as the amount of oxygen available for respiration in the water body for the organisms reduces.

Final answer

(b) Death of fish due to lack of oxygen