Variability of the United States Environmental Protection Agency's Rapid-Bioassessment Protocol III was examined by comparing the results of benthic macroinvertebrate surveys and habitat assessments conducted by 14 student groups on each of three distinct 2nd-order reaches of Strawberry Creek, on the Berkeley campus of the University of California: a reach that was recently restored to improve water quality and aquatic habitat; an unrestored tributary, which receives occasional inputs of organic pollution; and an unmodified reference site upstream of the restored site. Impact was assessed by comparison with the reference site using three different impairment thresholds: 83% similarity; 65% similarity; and the interquartile range of the reference-site data. A randomized block analysis of variance showed that taxa richness, the Family Biotic Index (FBI),% Ephemeroptera-Plecoptera-Trichoptera (EPT) abundance, EPT/Chironomidae abundance ratio, EPT/[Chironomidae+EPT],% contribution of dominant taxon, and% shre...