Rated based on the amount and variety of hard, stable substrates usable by benthic macroinvertebrates. Because they inhibit colonization, flocculent materials or fine sediments surrounding otherwise good substrates are assigned low scores. Scores are also reduced when substrates are less stable.
| Range | Category |
|---|---|
| 0 - 5 | Stable substrate lacking; or particles are over 75% surrounded by fine sediment or flocculent material |
| 6 - 10 | Large boulders and/or bedrock prevalent; cobble, woody debris, or other preferred surfaces uncommon |
| 11 - 15 | Abundance of cobble with gavel &/or boulders common; or woody debris, aquatic veg., under-cut banks, or other productive surfaces common but not prevalent/suited for full colonization |
| 16 - 20 | Preferred substrate abundant, stable, and at full colonization potential (riffles well developed and dominated by cobble; and/or woody debris prevalent, not new, and not transient) |