Biological condition assessment tiers, associated index scores, and generalized descriptions 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.

Assessment Tier	Approximate Range of Scores	Meets/Fails Virginia Regulatory Standard	Narrative Description
Very good	70 and over	Meets	Natural or nearly natural biological conditions: the benthic macroinvertebrate community is diverse. Many types of organisms are present. The majority of the population is intolerant of human-caused stresses.
Good	60-70	Meets	Somewhat degraded: The community is diverse. Many types of organisms are present, but the number of types of sensitive organisms is somewhat reduced. The majority of the population is intolerant of human-caused stresses.
Fair	40-60	Fails	Moderately degraded: The community is fairly diverse. Many types of organisms are present, but the number of types of sensitive organisms is reduced. The majority of the population is tolerant of human-caused stresses.
Poor	25-40	Fails	Substantially degraded: The community is much less diverse. 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	0-25	Fails	Severely degraded: The community contains very few types of organisms, virtually all of which are tolerant of human-caused stresses.