Bugs and Water Quality

waterpg3DID YOU KNOW you can tell the health of a stream by the critters living in it?


Macroinvertebrates are animals that have no backbone and are visible without magnification. Stream-bottom macroinvertebrates include such animals as crayfish, mussels, aquatic snails, aquatic worms, and the larvae of aquatic insects.





Stream-bottom macroinvertebrates are an important part of the community of life found in and around a stream.

Stream-bottom macro-invertebrates are a link in the aquatic food chain. In most streams, the energy stored by plants is available to animal life either in the form of leaves that fall in the water or in the form of algae that grows on the stream bottom. The algae and leaves are eaten by macroinvertebrates. The macroinvertebrates are a source of energy for larger animals such as fish, which in turn, are a source of energy for birds, raccoons, water snakes, and even fishermen.


Pouch snail
Pouch snail

Stream-bottom macroinvertebrates differ in their sensitivity to water pollution.

Some stream-bottom macroinvertebrates cannot survive in polluted water. Others can survive or even thrive in polluted water. In a healthy stream, the stream-bottom community will include a variety of pollution-sensitive macro-invertebrates. In an unhealthy stream, there may be only a few types of nonsensitve macro-invertebrates present.



Stream-bottom macroinvertebrates provide information about the quality of a stream over long periods of time.

It may be difficult to identify stream pollution with water analysis, which can only provide information for the time of sampling. Even the presence of fish may not provide information about a pollution problem because fish can move away to avoid polluted water and then return when conditions improve. However, most stream-bottom macroinvertebrates cannot move to avoid pollution. A macro-invertebrate sample may thus provide information about pollution that is not present at the time of sample collection.


Click on chart to download a larger version!

Source: Save Our Streams Monitor’s Guide to Aquatic Macroinvertebrates, by Loren Larkin Kellogg (Izaak Walton League of America, 1992)


Stephanie Harmon
Watershed Specialist
717-277-5275 ext. 114

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