How can high levels of bacteria from sewage pollution affect dissolved oxygen?

High levels of bacteria from sewage pollution can deplete dissolved oxygen (DO) in water bodies as these bacteria consume oxygen while breaking down organic matter. This process, known as biochemical oxygen demand (BOD), can lead to lower DO levels, which are essential for aquatic life. As oxygen levels drop, fish and other organisms may struggle to survive, resulting in decreased biodiversity and potential fish kills. Ultimately, this creates a harmful environment for aquatic ecosystems.