This study investigates seasonal variations in stream water quality and the potential influences of cloud-seeding experiments on stream chemistry. Since the winter of 2006, cloud-seeding operations have been conducted at the Daegwallyeong Cloud Physics Observation Center (CPOS), a high-altitude site in South Korea. Odaecheon-1, located approximately 17.6 km downstream from CPOS, was selected as a monitoring site due to its proximity to the experimental area and its suitability for capturing downstream hydrological responses. Long-term monitoring data from 1997 to 2024 were analyzed, focusing on four key water quality indicators: water temperature, dissolved oxygen (DO), pH, and electrical conductivity (EC). March and October were chosen as representative months to compare post-winter seeding conditions with pre-seeding seasonal baselines. The results show a distinct increase in water temperature and EC in March, accompanied by a decrease in DO and a slight decline in pH. These patterns were not observed in October, suggesting that seasonal shifts alone do not explain the March trends. The observed changes are likely influenced by the influx of snowmelt containing residual seeding materials such as silver iodide (AgI), sodium chloride (NaCl), and calcium chloride (CaCl2), which increase ionic content and alter stream chemistry. These findings suggest that cloud-seeding experiments may induce measurable changes in stream water quality, particularly during early thaw periods. The results underscore the importance of long-term water quality monitoring in regions affected by weather modification programs and offer a scientific basis for assessing the environmental impacts of cloud seeding in alpine watersheds.