Effects of contaminants on communities are difficult to assess and poorly understood. We analyzed in situ effects of trace metals and common environmental variables on benthic macroinvertebrate communities in floodplain lakes. Alternative measures of trace metal availability were evaluated, including total metals, metals normalized on organic carbon (OC) or clay, simultaneously extracted metals (SEM), combinations of SEM and acid-volatile sulfide (AVS), and metals accumulated by detritivore invertebrates (Oligochaeta). Accumulated metal concentrations correlated positively with sediment trace metals and negatively with surface water dissolved OC. Sixty-eight percent of the variation in benthic community composition was explained by a combination of 11 environmental variables, including sediment, water, and morphological characteristics with trace metals. Metals explained 2 to 6% of the community composition when SEM-AVS or individual SEM concentrations were regarded. In contrast, total, normalized, and accumulated metals were not significantly linked to community composition. We conclude that examination of SEM or SEM - AVS concentrations is useful for risk assessment of trace metals on the community level.