How can scientists determine if a waterway is contaminated with raw sewage?

The presence of coliform bacteria is a reliable indicator of contamination by raw sewage in a waterway. Coliform bacteria are a group of microorganisms found in the feces of warm-blooded animals, including humans. When raw sewage enters a waterway, it introduces these bacteria into the environment.

Detecting high levels of coliform bacteria is significant because it suggests the potential presence of pathogenic microorganisms that can pose health risks to humans and wildlife. Water quality testing for coliform bacteria provides a direct assessment of the microbiological safety of the water, thereby indicating whether it may be contaminated with sewage.

While other methods, like measuring pH levels, testing for heavy metals, and assessing dissolved oxygen levels, can provide information about water quality, they do not specifically indicate the presence of sewage contamination. pH levels can fluctuate due to various natural and anthropogenic factors, heavy metals may originate from a range of sources not solely linked to sewage, and dissolved oxygen levels can be affected by numerous ecological processes unrelated to sewage presence. Therefore, the detection of coliform bacteria is the most indicative method to confirm if a waterway has been contaminated with raw sewage.