Nitrogen (N2) is one ofthe most important ecosystem nutrients functioning as a limiting factor for their productivity. Nitrogen pollution can have negative ecological effects on the environment, including soil acidification, hypoxia and fish die-offs. A high concentration of nitrogen is the main cause of eutrophication of the aquatic environment, which results in the decrease in biological diversity and deterioration of water quality. High levels of nitrogen compounds in drinking water increase the risk of human disease emergence. Also, nitrogen overload is one of the main reasons for the deterioration of surface water quality. Therefore, monitoring its concentration is essential for maintaining good surface water quality. Human activities have greatly accelerated the input of nitrogen into water systems, resulting in their degradation. In this paper, surface water samples were analyzed, i.e. total nitrogen concentrations were determined in the area of Varaždin and Krapina-Zagorje counties in the six-month period from November 2022 to April 2023. LCK 138 cuvet tetests were used to determine the concentration of total nitrogen in individual water samples. The results show that 5 locations are in accordance with the Regulation on Water Quality Standardsand the State of Surface Water Bodies, i.e. that the concentration values of the total amount of nitrogen are within the prescribed limit values. The concentrations of the total amount of nitrogenin surface water at the other locations are higher than the prescribed limit values of 2 mg/l N.