Villarrica Volcano (Chile) is one of the most active volcanoes of South America, and eruptions often generate volcanic mudflows (lahars) due to its perennial snow cover. The final goal of this research is to reconstruct the Holocene snow cover from hydrogen isotopes of biomarkers in lake sediments. Linking this climate record to the volcanic activity and lahar record will indicate if and how climate change influences the lahar hazard. However, interpretation of water isotopes requires a good understanding of the environment (hydrological cycle, vegetation…). Here, we focus on understanding seasonal isotopic changes in rain, snow, river and lake water by monthly monitoring (since June 2024), supplemented by sampling of the stratified lake water during austral summer to determine the signal from algal blooms, as well as soil samples to fingerprint the terrestrial sources. Finally, short cores will be obtained to map the spatial hydrogen isotope variability in biomarkers across the lake.