Main goal of our diploma work was the assessment of factors threatening quality of water flows with emphasis on the characteristics and influence of endocrinal disruptors and polychlorinated biphenyls in aquatic environment. Endocrinal disruptors present a complex of various chemicals, including polychlorinated biphenyls. In aquatic environment, certain concentrations of the chemicals may cause perishing or other danger to whole aquatic life. In case of some kinds of fish, the presence of the chemicals may result in different abnormalities like intersexuality. Another goal of the paper, using collected data, is assessment of the procuring cause of mass fish kill in Slovakia, specifically catchment area of middle and upper flow of river Hron. In these areas, there were various causes of mass fish kill observed, such as high temperatures, insufficient amount of dissolvable oxygen in water, excessive amounts of copper or high values of iron. In one specific case, in Neresnica water flow, there has been a significant cause of fish kill observed, in which by excercising virological examination, viral haemmorhagic septicaemia and infectious hematopoietic necrosis have been confirmed. Resolving environmental load in Slovakia and abroad is another goal of our diploma work. One of the significant solutions of this situation in Slovakia is the recording of harmed areas through Informational system of environmental loads, originally Informačný systém environmentálnych záťaží (ISEZ), and creating national decontamination program, originally Štátny program sanácie environmentálnych záťaží (ŠPS EZ), for a specific period, with both short- and long-run solution targets. Fundamentals of damage recompensation of impacted areas in Slovakia and abroad is, that if the culprit is known, he is liable for the damage. However, the culprit remains unknown in all of the areas mentioned above.