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The invertebrate community you find at a particular site is shaped by a combination of physical habitat and water quality factors.

There are many “sensitive” taxa that are strongly associated with “natural” (typically bush-covered) habitats with good water quality, and there are several “tolerant” taxa that can thrive in highly modified streams with poor water quality.

The presence of tolerant taxa in a sample does not necessarily mean the stream is in poor condition because most tolerant taxa can survive quite happily in high quality and poor quality streams.

It’s better to assess a community using the numbers of “sensitive” taxa and their abundances in your sample (or the proportion of the community made up of sensitive taxa).

The tolerance values (ranging from 0 to 10) listed in the Identification guide give an indication of which are the sensitive taxa (values of 8 or more) and which are the tolerant taxa (values of 3 or less). Some examples of sensitive and tolerant taxa are shown below: