What environmental impact can untreated sewage have?

Untreated sewage can have a significant detrimental effect on the environment, particularly leading to the contamination of waterways and harm to aquatic life. When untreated sewage is released into water bodies, it introduces a variety of pathogens, nutrients, and harmful chemicals. This pollution can result in the depletion of oxygen in the water, leading to conditions that are unlivable for many aquatic organisms. Moreover, the influx of nutrients from sewage can stimulate excessive algal blooms, which can further deplete oxygen levels and create dead zones where aquatic life cannot thrive. The presence of pathogens can also pose a risk to human health and disrupt the balance of local ecosystems, causing long-lasting environmental consequences.

The other options are not consistent with the well-documented impacts of untreated sewage. For example, untreated sewage does not improve soil quality; rather, it can lead to soil contamination. Additionally, while untreated sewage can negatively affect wildlife, it does not directly reduce their immune systems nor does it enhance recreational water quality—in fact, it typically has the opposite effect, making water unsafe for recreational use.