Abstract
This paper presents an extended analysis of the long-term dynamics of the pH index in the surface waters of the Tikhaya River (East Kazakhstan Region) for the period 2017...2025. The study covers both monthly and annual averages, as well as intra-seasonal and interannual pH fluctuations. Statistical and graphical visualization methods have been applied, including thermal mapping, span diagrams, and linear regression approximation. Trend analysis was also performed using linear regression models, and a heat map of clustering by month was constructed. It was found that the pH of the river waters fluctuates within the limits of a slightly alkaline reaction, without stable signs of acidification. At the same time, some anomalies have been identified, especially in summer, due to natural and anthropogenic factors. The presented data indicate a high buffering capacity of the reservoir and its ability for ecological self-regulation.