Question

Fishes die by sewage because

• A. Of its bad smell.
• B. It replaces food material of fishes.
• C. It increases oxygen competition among fishes.
• D. $C{O}_2$ is mixed in large amount in water.

Answer 1

The correct option is C It increases oxygen competition among fishes.

Sewage discharge in water bodies leads to organic loading or occurrence of excess organic matter inside water body. Its putrefaction decreases dissolved oxygen leading to competition for oxygen among fishes. Also blue green algae bloom and increase in number and release toxins. Both toxicity and decreased oxygen level kill aquatic animals, like fishes.