This article presents the results of a comprehensive environmental assessment of surface water quality in the tourist regions of the Ivano-Frankivsk oblast, with a case study of the upper Prut River within the city of Yaremche. Given the intensification of seasonal recreational activities in the Carpathian region, special attention is paid to the ecological condition of mountain water bodies and their natural self-purification capacity. The study applied modern mobile express methods using a multifunctional portable water-quality meter (AZ 8603K) to conduct in situ measurements of key hydrochemical parameters, including total mineralization, pH, and dissolved oxygen (DO) concentration. Field sampling was carried out at ten control points along a 90-meter river section downstream from the Probiy waterfall - a zone of high turbulence and anthropogenic pressure. The data revealed a sharp decrease in mineralization (from 700 to 251 mg/L) and a simultaneous increase in DO (from 40.9 to 93.3 mg/L) within the first 30 meters, demonstrating the efficiency of turbulent aeration, dilution, and gravitational sedimentation. To quantitatively describe this self-purification process, an exponential decay model M(x) = 450·e⁻⁰.⁰⁷x + 250 was developed, capturing the spatial attenuation of mineralization and confirming stabilization beyond the initial turbulent zone. In parallel, an emission-based approach was used to estimate pollutant loads (BOD₅, nitrogen, phosphates) from both the permanent population (23,165 residents) and annual tourist flows (approx. 1 million visitors). The results indicated that the seasonal tourist load generates up to 43 times higher pollutant emissions than local residents, underscoring the critical environmental vulnerability of high-tourism mountain basins. A comparative analysis of field results with systematic state monitoring data (State Agency of Water Resources of Ukraine) confirmed the reliability of mobile diagnostics and highlighted the need for adaptive water quality management in regions with seasonal ecological stress. The findings demonstrate the feasibility of integrating mobile express monitoring, mathematical modelling, and emission forecasting into national water governance frameworks. The study provides scientifically grounded recommendations for improving environmental safety in tourist areas, including the modernization of wastewater treatment infrastructure, the development of mobile purification units, and stricter regulation of diffuse pollution sources.