The Pollution Index

The Pollution Index is used to determine the level of organic pollution by studying the kinds of algae in a sample of water. On the Pollution Index Chart, a Pollution Index factor of 1 to 5 is assigned to each of the 20 types of algae that are most tolerant of organic pollution. The most tolerant types are assigned a 5. The less tolerant the algae is, the lower the number it is assigned.

Pandorina (1)

Oscillatoria (5)

The amount of algae, as well as the types of algae present, are indicators of water quality. Batrachospermum, for example, is an indicator of clean water because it lives only in cold water with low levels of organic pollution. Clean water has a low population of algae with high diversity, whereas polluted water has a high population of algae with low diversity.