This paper presents the results of monitoring the content of thiols in the Ichel River. Thiol concentrations were determined using the Ellman method. To assess the effect of humic acids on the content of thiols in water, monitoring was carried out using unfiltered and filtered water. Correlation coefficients between thiol content and parameters such as temperature and BOD were also calculated. According to the data obtained, the presence of humic acids in water leads to a decrease in the content of thiols, which is due to their adsorption. It was also found that thiols in the Ichel River are the waste products of hydrobionts, and do not enter the river as a result of anthropogenic impact. Despite the natural origin of thiols, the average annual BOD values indicate that the waters of Ichel are moderately polluted and that other classes of substances of anthropogenic origin are present in the waters.