Ontario Operator-in-Training Practice Exam 2025 – Complete Study Resource

The environmental issue that can arise from the discharge of raw sewage is oxygen depletion and the potential death of aquatic life. When raw sewage is released into water bodies, it introduces a substantial amount of organic matter and nutrients, such as nitrogen and phosphorus. The presence of these substances promotes the rapid growth of bacteria that utilize dissolved oxygen in the water for decomposition.

As bacteria consume this organic material, they deplete the dissolved oxygen levels in the water, creating conditions that are unsuitable for many aquatic organisms, including fish and invertebrates. When oxygen levels drop below critical thresholds, it can lead to hypoxia (low oxygen conditions), which can stress or even kill aquatic life, ultimately disrupting the entire ecosystem. These changes in the aquatic environment not only harm individual species but can also lead to broader ecological imbalances.

In relation to the other options, increased oxygen levels would be the opposite effect of what typically happens with raw sewage discharge. Decreased sedimentation may occur in specific contexts but is not a direct or common result of sewage discharge. Wastewater purification is intended to avoid the problem associated with raw sewage by treating it before it enters water bodies, preventing the detrimental effects on aquatic ecosystems.