Most anthropogenic stressors affecting freshwater systems are qualitatively known. However, the quantitative assessment of contaminant exposure and effects to aquatic communities is still difficult, limiting the understanding of consequences on aquatic ecosystem functioning and the implementation of effective management plans. Here, multisubstance indicators based on caged gammarid bioaccumulated contamination data are proposed (for metals and persistent organic pollutants, POPs) to map the bioavailable contamination level of freshwater ecosystems at a large spatial scale. We assessed the ability of these indicators to highlight the relationships between chemical exposure gradients and alteration in the abundance of macroinvertebrate populations on a data set of 218 watercourses distributed throughout France. We identified spatial regional heterogeneities in the levels of bioavailable contamination of metals (18 compounds) and POPs (43 compounds). Besides this, a degradation of Gammaridae, Ephemeridae, and Hydrobiidae densities with increasing levels of metal contamination are identified relative to Baetidae, Chironomidae, and Hydropsychidae. We show here that active biomonitoring allows the establishment of multisubstance indicators of bioavailable contamination, which reliably quantify chemical exposure gradients in freshwater ecosystems. Our ability to identify species-specific responses to chemical exposure gradients demonstrates the promising possibility to further decipher the effects of chemical contamination on macroinvertebrate assemblages through this type of indicator.