Distinguishing between effects of natural and anthropogenic environmental factors on biological communities is a fundamental problem in bioassessment. Effects of organic toxicants at moderate concentrations (e.g., pesticides released during normal agricultural practice) are hardly detectable due to environmental factors, which confound and mask the community alterations caused by these contaminants. The Species At Risk (SPEAR) concept was developed as a trait-based indicator for distinguishing pesticide effects on macroinvertebrates from the influence of other environmental variables (Liess & Ohe 2005 Environ. Toxicol. Chem. 24: 954-965). In this system a set of biological traits related to toxicant effect and recovery is used. These traits are sensitivity to organic toxicants (S_organic), generation time, migration ability, and presence of aquatic stages during the time of maximum exposure to pesticides. Sensitivity to organic toxicants S_organic is a taxon-specific physiological measure found in laboratory toxicological tests. Application of the SPEAR has shown that this system is specifically sensitive to moderate pesticide contamination when conventional ecological indexes are not effective. Additionally, it was shown that average community sensitivity S_organic is independent of natural longitudinal environmental factors and sensitive to contamination with organic toxicants. The case studies in several geographical regions are discussed.