A method for describing water quality using characteristics of
aquatic communities, such as the types of fish and invertebrates
found in the water body. It is expressed as a numerical value
between 0 (lowest quality) to 100 (highest quality).
Glossary Term Category
Glossary Term Show In Main
Yes
Glossary Term Ext Def
IBI Ratings are defined as follows:<br><br>
<b>Excellent</b>: Comparable to the best situations with minimal
human disturbance; all regionally expected species for habitat
and stream size, including the most intolerant forms, are present
with a full array of age and size classes; balanced trophic
structure.<br>
<br>
<b>Good</b>: Species richness somewhat below expectations,
especially due to the loss of the most intolerant forms; some
species are present with less than optimal abundance's or
size/age distributions; trophic structure may show signs of
imbalance.<br>
<br>
<b>Fair</b>: Signs of aquatic community changes include decreased
species richness, loss of intolerant forms, reduction in simple
lithophiles, increased abundance of tolerant species, and/or
highly skewed trophic structure (e.g., increasing number of
omnivore species and less specialized feeding species); older age
classes of top carnivores rare or absent. <br>
<br>
<b>Poor</b>: Relatively few species; dominated by tolerant forms,
habitat generalists, and omnivores; few or no top carnivores or
simple lithophilic spawners; growth rates and condition factors
sometimes depressed; hybrids sometimes common.<br>
<br>
<b>Very Poor</b>: Very few species present, mostly tolerant
forms, hybrids, or exotics; few large or older fish; DELT fish
(fish with deformities, eroded fins, lesions, or tumors)
sometimes common.