The aim of this study is to determine the impact of water quality upon lipid, protein oxidation and DNA damage in the tissue of farmed Oncorhynchus mykiss (Walbaum, 1792) in concrete pond farms located in Candir River (Station I), Karacaoren 1 Reservoir (Station II), and catak Reservoir (Station III). The O. mykiss muscle tissue, blood and water samples were obtained simultaneously from all stations on February 2016. For each station, fourteen physicochemical parameters were measured in water samples and water quality levels determined by YSKYY (Surface Water Quality Management Regulation) were recorded. Muscle tissue malondialdehyde (MDA), protein carbonyl (PC) levels, and grade of DNA damage in erythrocytes using comet assay were determined in 0 mykiss from three fish farms. The water's physical and chemical parameters show that based on Turkish YSKYY, the water in all stations are categorised as class II according to the Turkish YSKYY. However, based upon its nitrite and total nitrogen values, Station III was found to be less polluted than the other stations, followed by a moderate degree of pollution for Station II, and significantly higher levels or pollution for Station I. The MDA and protein carbonyl levels were significantly higher in the muscle of the O. mykiss from Station I than Station II and III (p<0.01). Fish from Station I exhibited a significantly higher DNA damage in red blood cells than Station II and Station III (p<0.01). The study concluded that nitrogen species caused by exposure to an accumulation of environmental pollutants are an important source of RNS/ROS generation within the fish's tissue. RNS/ROS-mediated oxidative stress causes DNA fragmentation, lipid oxidation, and protein dysfunction, consequently negatively contributing to the quality of fish as a source of food, and also to their welfare.