1) What are we looking for in the streams?

A dip net is used to sample the stream bottoms to collect insects, mollusks, and crustaceans that are collectively called "macroinvertebrates."  These benthic (bottom-dwelling) invertebrates are organisms that can easily be seen with the naked eye and their presence is an indicator of the stream's water quality.  Certain families are more tolerant to pollution than others. Their ability to withstand poor water quality is given a number called  Family Tolerance Value (FTV).  This numeric value is based on a scale of 0 being the most sensitive to pollution and 10 being the most tolerant to pollution.  Click on the table below to see how tolerant your favorite macroinvertebrate is to pollution based on its Family Tolerance Value.


  • Coleoptera (Beetles)
  • Trichoptera (Caddisflies)
  • Ephemeroptera (Mayflies)
  • Odonata (Dragonflies and Damselflies)
  • Plecoptera (Stoneflies)
  • Hemiptera (True Bugs)
  • Megaloptera(Fishflies, Dobsonflies, Alderflies)
  • Diptera (True flies)
  • Lepidoptera (Moths and Butterflies)
  • Isopoda (Sowbugs) Amphipoda (Scuds)

2) What do the macroinvertebrates look like?

Macroinvertebrates (PDF Document)

3) How are the streams rated?

The final stream score is totaled using the variety of insects, the number of insect families present in the sample that are intolerant to pollution, the family with greatest number of individuals and the family tolerance values. The final score is compared against the following biological assessment table:

Non-impaired:  Benthic community comparable to other undisturbed streams within the region.  A community characterized by a maximum taxa richness, balanced taxa groups and good representation of intolerant individuals.

Moderately Impaired: Macroinvertebrate richness is reduced, in particular EPT taxa. Taxa composition changes result in reduced community balance and intolerant taxa become absent.

Severely Impaired: A dramatic change in the benthic community has occured. Macroinvertebrates are dominated by a few taxa which are very abundant. Tolerant taxa are the only individuals present.

Biological Assessment NJIS Score
Non-impaired 24-30
Moderately Impaired 9-21
Severly Impaired 0-6

Page Last Updated: 2/6/2008 10:46:00 AM

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