A river receives a large discharge of untreated sewage. Which of the following best explains why the fish population in that section of the river decreases?

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Question

A river receives a large discharge of untreated sewage. Which of the following best explains why the fish population in that section of the river decreases?

Accepted Answer

B) Bacteria decomposing the sewage use up dissolved oxygen, suffocating the fish — When sewage enters a river, aerobic bacteria decompose the organic matter and consume large amounts of dissolved oxygen in the process. This reduces oxygen concentration in the water to levels too low for fish to survive, a process called biological oxygen demand (BOD). Fish do not drink water in the same way, nor is light the primary issue.

Answer

B) Bacteria decomposing the sewage use up dissolved oxygen, suffocating the fish

Answer

C) The sewage blocks sunlight, preventing fish from seeing their prey

Answer

D) Fish migrate upstream to avoid the smell of the sewage

Answer

A) Fish are directly poisoned by the sewage chemicals they drink

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