On the basis of the analysis of wide temporal monitoring data, a forecast of the integrated hydrochemical indicators of the waters of the Inhul river (Ukraine) was carried out. The performed analysis was also the basis for the determination of a mathematical model of natural fluctuations of the indicators studied. The determined sinusoidal dependence of the integrated water quality indicators allowed determining the average time of fluctuations concerning the processes of self-organisation of river waters. In practice, the developed mathematical models may constitute a valuable support and supplement to the existing models in the field of prediction of self-organization processes of river waters. They may also contribute to even more effective minimization of undesirable effects of anthropogenic impact on aquatic ecosystems.