The upper stretch of the Pek River is located in proximity to one of the largest mining sites in Serbia. To estimate the influence of copper mining on river biota, the quantitative and qualitative macroinvertebrate community structure was analyzed, and the ecological status of the river was assessed using standard biological indices. Data was gathered at 6 sites along the river. A total of 75 macroinvertebrate taxa were recorded. The reference site had the highest number of recorded taxa (48) and a high biodiversity (diversity index H=2.3). In contrast, the lowest number of taxa (8), a low diversity index value (H=1.15), and a very poor overall ecological status were recorded at site 2, which is heavily influenced by mining discharge. The Ephemeroptera, Plecoptera and Trichoptera group (EPT) constituted 46.30% of the community at site 1 but was completely absent at site 2 where Diptera (70%) and Oligochaeta (20%) were dominant, reflecting a strong impact of the mining industry on the upper river stretch. A gradual improvement of water quality downstream of the pollution sources indicates that this medium-sized river has the capacity to overcome intensive pollution and to revitalize itself along its course.