Any biological entity or process, or community whose characteristics show the presence of specific environmental conditions or pollutants. Good indicators of water pollution are the contaminants found within that source of water. If there is a presence of extreme pH, metallic ions, stagnation, elevated levels of sulphur, colloids, algae blooms, and other contaminants then the water is most likely experiencing issues of pollution. Pathogenic germs such as viruses, bacteria and leeches are also good indicators of contamination occurring in the drinking water and should be treated before further use.