Trout production represents one of the major agricultural activities in Serbia. Organic compounds are drained into the environment usually without previous sedimentation, thus affecting the stream biota. Considering that biological monitoring is commonly based on aquatic macroinvertebrates as target organisms, we used larvae of Dinocras megacephala to estimate trout farm effects on mass of the larvae and their antioxidative defense in pollution stress conditions. Four localities were chosen along the channel of the Raška river, two upstream (L1, L2) and two downstream (L3, L4) from the trout farm outlet. Basic physical and chemical water parameters were measured. Superoxide dismutase (SOD) and catalase (CAT) activity changes were analyzed in order to determine the level of oxidative stress caused by the increase of organic compounds originating from the trout farm. Dissolved oxygen concentration decreased from the upstream to downstream localities. Also, the concentration of ionized ammonia was almost ten times higher at the downstream localities than at the upstream ones. Larval mass, as well as CAT activity, was significantly higher at L3 as compared with the other three localities. Activity of SOD was significantly higher at L3 than at L1. The results indicate that higher concentrations of organic compounds from the trout farm induce clear changes in the status of the antioxidant defense of D. megacephala larvae. This article is protected by copyright. All rights reserved.