The study of oil-oxidizing bacteria number and activity has been carried out for the first time in contaminated with oil products and relatively clean areas of Zaporozhskoye reservoir in spring 2014. The research showed high potential oxidative capacity (POC) of water microflora that probably corresponds to the level of water pollution with oil products. During spring season the spatial distribution of oil bacteria as well as dependence on sampling time and water temperature were studied. Analysis of spatial distribution of oil-oxidizing bacteria numbers allowed to perform ranking of the sites with increasing bacteria numbers in direction from the site "Near Kodaki water draw-off" to "Monastyrskiy island". Distribution of oil-oxidizing bacteria observed during the period of study reflects pollution and self-cleaning state of the sites. Using correlation analysis conclusion about connection of oil-oxidizing bacteria with diatoms "bloom" in spring has been made that shows importance of "bloom" for the realization of bacteria role in the reservoir selfcleaning. The results are important for understanding the mechanisms of maintaining Zaporozhskoye reservoir ecosystem stability as well as for forecasting of pollution and self-purification processes and in general for the development and implementation of natural and artificial ecosystems sustainable development.