Anthropic activities can cause alterations in physical, chemical and biological characteristics of aquatic ecosystems. Therefore, this work shows an assessment of water quality of a stream that receives fish farming effluents, using insects as bioindicators. Aquatic insects were sampled in summer and winter of 2012, in three sites (upstream – P01; in the effluent discharge site – P02; downstream – P03) of Felizardo Stream, Uruguaiana, Brazil. Network lock, drift nets and dip nets were used for insect capture, and aquatic physical-chemical parameters (temperature, dissolved oxygen, ammonia nitrogen, electric conductivity, and pH) were analyzed. In the summer, differences about family richness, abundance and density of specimens were observed, with the P02 site values lower than P01 and P03, and higher degree of dominance than P01 and P03. The physical-chemical parameters were in accordance with allowed values, according with legislation. However the biotic indices suggest the occurrence of direct influence of fish farming effluents in insect fauna in P02. Therefore, there is evidence of moderate effects of water pollution, or some organic pollution, according with these biotic indices. With these results, the waters of Felizardo Stream remain in the class II, even suffering influence of fish farming effluents.