What is the primary problem associated with high levels of bacteria in waterways due to wastewater discharge?

High levels of bacteria in waterways, particularly when stemming from wastewater discharge, primarily lead to decreased oxygen levels in the water. This phenomenon occurs because bacteria consume oxygen as they break down organic matter found in wastewater. When large quantities of bacteria proliferate, they can significantly reduce the dissolved oxygen levels in the surrounding water.

Dissolved oxygen is crucial for aquatic life, including fish and invertebrates. When the oxygen levels drop below critical thresholds, it can lead to hypoxia, a condition where aquatic organisms cannot survive. This can result in fish kills as these organisms simply cannot breathe, leading to wider ecological and economic impacts.

While other options might touch on valid concerns associated with wastewater discharge, the primary and most immediate issue connected with elevated bacteria levels is the depletion of oxygen in the water, directly impacting the health of aquatic ecosystems.