Abstract. Lakes are ideal sites to study environmental changes since they preserve climatic, anthropogenic, and volcanic signals in their sediments. Brazo Blest is one of the most important ramifications of Lake Nahuel Huapi and it is an interesting site to study climatic variations as it receives direct discharge of heavy suspended sediments loads from Tronador Glacier through the Frias River, as a result of the abrasion of the bedrock and runoff from the surrounding Valdivian Forest. A short sediment core from Brazo Blest was analyzed for chironomid and diatom assemblages and pigments in order to reconstruct environmental changes during the last 100 years in the basin under study. This multiproxy study also included geochemical and physical analyses and reveals changes in the productivity of the lake over time, showing a shift in the 1950s from autochthonous to allochthonous organic matter. This modification is related to the increase of precipitation and the consequent fluvial runoff from two catchment...