Macroinvertebrates as Indicators of Water Quality

Posted: January 14, 2013

The importance of biological parameters as indications of the health of the river is highlighted in the State of the Susquehanna Report, but the principles are applicable to any stream or river.
Macroinvertebrate sampling. Photo courtesey of EPA

Macroinvertebrate sampling. Photo courtesey of EPA

Macroinvertebrates have long been used as indicators to assess water quality. “The aquatic resources and supporting habitat throughout the Susquehanna River Basin are important indicators of the health of the ecosystem and in turn, the quality of waters used for human water supply. Furthermore, the aquatic ecosystem supports many recreational activities such as hunting, fishing, trapping, nature study, wildlife photography, bird watching and eco-tourism.” (State of the Susquehanna)

A well-balanced and functioning biological community is one of the best indicators of a healthy stream, capable of providing vital ecosystem services. Benthic macroinvertebrates (bottom-dwelling organisms including aquatic insects, crayfish, clams, snails, and worms) are often used in studies to determine the quality of waters because of their high numbers, known pollution tolerances, limited mobility, wide range of feeding habits, varied life spans, and dependence on the land environment around the stream. When chemical grab samples are taken, they are really a snapshot of the water at that moment, that can change rapidly, but the macroinvertebrates are living there all the time. Their composition will be affected by either periodic episodes of poor water quality or continuous poor water quality.

Many watershed monitoring programs include biological indicators as well as chemical and physical tests. 

Macroinvertebrate studies are fun! The most interesting time spent in stream studies is often spent in the stream, looking under rocks. It is a great way to create a sense of interest and connection if introducing watershed stewardship to youth. The 4-H Stream Team materials are a great way to introduce youth to watershed stewardship.

A good tool to use when looking at stream macroinvertebrates is the Biotic Index Card that provides a key to identify invertebrates and information on interpreting the index. There is also a new video from the Susquehanna Basin Commission biologists demonstrating some invertebrate sampling techniques.

So when looking at water quality, take a look at the organisms that make the stream their home.

Contact Information

Diane Oleson, M.S.
  • Extension Educator, Renewable Natural Resources
Phone: 717-840-7429