Dissolved oxygen (DO) is the amount of O2 that is present in water and it is found in molecular state. Water bodies receive oxygen from the atmosphere and from aquatic plants. Running water, such as that of a swift moving stream, dissolves more oxygen than the still water of a pond or lake. Dissolved O2 levels change according to the temperature, air pressure and salinity. It is consumed not only by the reduction of substances such as sulphides, nitrites and iron ions, but also by the respiration of microorganisms and the oxidative decomposition of organic substances by aerobic microorganisms. The aim of this research is the analysis and classification of DO at the Hydrological Station G. Giannouli (HSG) of the Pinios river in central Greece, with the development of robust Machine Learning models. The results clearly demonstrate that these models can successfully assign five labels based on the thresholds established by the Norwegian Water Research Institute namely: “Poor”, “Deficient”, “Moderate”, “Good” and “High”.