Associate Safety Professional Practice Exam

What is the main reason for fish kills in streams by pollution?

1. Depletion of oxygen

2. Excessive sediments

3. Chemical runoff

4. High temperatures

The correct answer is: Depletion of oxygen

The depletion of oxygen in streams is the primary reason for fish kills related to pollution. When pollution enters water bodies, it often leads to an increase in organic matter. The decomposition of this organic matter consumes dissolved oxygen, a critical element for aquatic life, particularly fish. As oxygen levels drop, many fish species are unable to survive, leading to significant fish kills. Other factors, such as excessive sediments, chemical runoff, and increased temperatures, can contribute to poor water quality and fish deaths. However, these tend to have more indirect effects or can exacerbate conditions that lead to oxygen depletion. For example, while chemical runoff can introduce toxic substances into the water, it is often the subsequent decrease in oxygen levels that poses the most immediate threat to fish populations. Similarly, high temperatures can reduce oxygen solubility in water, further compounding the problem but not being the primary cause in themselves. Therefore, oxygen depletion stands out as the fundamental reason for fish kills linked to water pollution.