The aim of this thesis was to show the impact of Rijeka oil refinery wastewater on the marine environment, based on the analysis and processing of data from official reports for 2019. and 2020. The concentrations of parameters for wastewater, emissions of pollutants at Outfall 1, compared concentrations of physico-chemical indicators of environmental pollution with maximum permissible concentrations (MDK) according to the Environmental Permit, average concentrations of pollutants for sediment, estimated toxicity of heavy metals and PAHs in sediment according to the criteria for assessment, established relationships of total concentrations of PAHs and the share of carcinogenic PAHs in the sediment, and compared the physical and chemical indicators of sea pollution with prescribed limit values for seawater. The results for wastewater, sediment and seawater in the area of the Rijeka oil refinery for 2019. and 2020. confirm the conclusions of European studies that the waste water of the refinery is getting cleaner every year and has less impact on the marine environment.