Summary #
Different macroinvertebrate species have different tolerances for pollution. By identifying which organisms are present in a stream, you can infer the level of water quality. This page explains pollution tolerance ratings and how they are used in biological assessments.
Some organisms are very sensitive to pollution and will only inhabit clean, unpolluted water. Large numbers of these sensitive organisms indicate that the waterway is in good health. Other groups of organism are somewhat tolerant of pollution to very tolerant. As numbers of the pollution tolerant organisms increase and sensitive populations decrease, the health of the stream becomes is more precarious. Healthy streams have a diverse mixture of all groups, pollution sensitive and tolerant.
Pollution sensitive indexes have been developed for many organisms found in and around the waterways: insects, fish, algae, mussels, and bacteria. These indexes allow you to determine the health of the stream by surveying the population of organisms and calculating a Pollution Tolerance Index.
Sources/Links (as provided in the source text):
Related Pages #
- Developing a Monitoring Plan
- Water Quality — What biological monitoring tells us
- Collection Methods — How to collect biological samples
- Macroinvertebrate Guide — Identifying stream organisms
Source and Last Reviewed #
Source: AMR Clearinghouse (amrclearinghouse.org). Migrated to AML-Connect. Last Reviewed: 2026-03-13.
[Admin note: Some external links in this article may be outdated. Verify before relying on them. Flag dead links for removal or replacement.]
Tags: monitoring, sampling, education
