Mentum deformities in Chironomidae communities as indicators of anthropogenic impacts in Swartkops River

► Results provide evidence of possible toxic contamination of the Swartkops River. ► Seasonality does not significantly affect the expression of mentum deformities. ► Results highlights importance of screening deformities in all sampled chironomids. ► Results provide evidence of sub-lethal effects of pollution on chironomid larvae.