Climate change, with its impact on water resources, highlights the need for effective monitoring tools. Satellite altimetry, exemplified by Sentinel-3A/B, provides an instrument to estimate lake levels, fundamental for understanding climate events. This study explores the application of satellite altimetry, specifically using the AlTiS software, to analyze the water level of Lake Ranco in south-central Chile from 2020 to 2023. The research aims to contribute valuable insights for water resource management and policymaking. The AlTiS software processes radar altimetry data, producing a time series of water levels. The study integrates in-situ records from the General Water Directorate of Chile for validation. The results demonstrate a strong correlation between altimetry-derived lake levels and observed in-situ data, with a mean square error of 0.12 m and a Kling Gupta Efficiency of 0.85. Analysis of meteorological trends reveals a slight increase in precipitation and a temperature decrease since 2015 in the Lake Ranco basin. The successful application of satellite altimetry in this study underscores its significance for water resource management, providing a reliable tool for lake administration and policy formulation.