Pharmaceutically active compounds (PhACs), in particular, nonsteroidal antiinflammatory drugs (NSAIDs) are in increasingly wider usage, and as such are more and more frequently part of the organic matter of recipient rivers, especially in their lower courses. To indicate their significance as pollutants, as well as the significant role that the presence of autochthonous microflora plays in solving this issue, we undertook to perform this experiment. The experiment, titled ?Application of the model of cylindrical reactor in self-purification by indigenous microorganisms?, was conducted during a one-year period at the location of Vukovci, in the lower course of the Moraca river. Assuming that the concentration of NSAIDs and PhACs in water can be reduced through selfpurification, it has been proven that such processes result in a modification of phenotype in the indigenous microbiological population. Having the abovementioned premise in mind, we constructed the experiment model, which entails kineticism of water, whereas the defined volume flow rate per unit time was 0.005 m/s, through the known distance of 432 m. Over one year of application of the model of the cylindrical reactor for enhancing self-purification capacity by indigenous microorganisms, auto-purification increased by 28.05%, the phenotype of the indigenous microorganisms changed by 24.62%, whereas the total concentration of particular PhACs, micropollutants, and NSAIDs decreased by 4.19%.