2006 Assessment. Generalized description of macroinvertebrate communities associated with health tiers. These are not criteria, but rather descriptions based on averages calculated from many samples. Characteristics of individual samples can vary.

Very good	Approaching natural conditions. The community is diverse. Many types of organisms are present. The majority of the population is intolerant of human-caused stresses.
Good	Slightly degraded. The community is diverse. Many types of organisms are present, but the number of types of sensitive organisms is somewhat reduced relative to the “very good” community. The majority of the population is intolerant of human-caused stresses.
Fair	Moderately degraded. The community is fairly diverse. Many types of organisms are present, but the number of types of sensitive organisms is reduced relative to the “very good” community. The majority of the population is tolerant of human-caused stresses.
Poor	Substantially degraded. The community is clearly less diverse than “very good” communities. Fewer types of organisms are present, and the number of types of sensitive organisms is deeply reduced. The great majority of the population is tolerant of human-caused stresses.
Very poor	Severely degraded. The community contains very few types of organisms, virtually all of which are tolerant of human-caused stresses.