Final answer:
Releasing sewage into water bodies is concerning because it depletes oxygen needed by aquatic life due to eutrophication, contributes to waterborne diseases, and creates dead zones.
Step-by-step explanation:
It is a concern if sewage is released into water bodies because sewage will deplete the water of oxygen required by fish and other animals. Sewage contains organic matter and nutrients like nitrogen (N) and phosphorus (P), which support the excessive growth of algae and microorganisms in a process known as eutrophication. This can lead to oxygen depletion (anoxia), causing what are known as dead zones where aquatic life cannot survive. Additionally, untreated sewage is a source of pathogenic microorganisms, which can cause waterborne diseases, affecting both aquatic life and humans. Therefore, proper sewage treatment is necessary both for preserving water quality and for public health.