When domestic sewage mixes with river water, is the river water still suitable for drinking?

When domestic sewage mixes with river water, the microbes present in the water start to degrade it. This increased microbial activity increases the biological oxygen demand (BOD) of the water. As the percentage of dissolved oxygen decreases, it leads to the death of aquatic life. So, the correct answer is option B (The increased microbial activity uses up dissolved oxygen), although option D is also a consequence of the decreased oxygen levels. The statement that the river water is still suitable for drinking is incorrect because the sewage introduces pathogens and pollutants that make it unsafe for consumption.