It is well-established that changes in climatic conditions across Alpine environments have influenced tree-growth at altitudes close to the tree line. Less well-known is the impact that increasing proportions of glacial melt water, which may accompany increasing temperatures and otherwise drier conditions during warmer summers, have on the tree growths along the glacial outwash rivers within the basin. In Switzerland many of these glacial melt water fed basins are also used for hydropower generation, hence further influencing the drainage patterns within such basins. This study focuses on the Turtmann River Basin in south-west Switzerland where an upstream hydropower dam (2,200 m above mean sea level) extracts glacial melt waters, with the riverine flow below the dam becoming increasingly dominated by snow melt and/or rainfall from the unglaciated and unexploited catchment. The influence of a change in climate as well as the impacts of the added hydroelectric scheme on the regional hydrology in the Turtmann basin was assessed by examining the whole wood tree ring stable isotope compositions of Larix decidua located both proximal and distal to the river at selected sites within the Turtmann catchment. Oxygen and hydrogen isotope compositions of earlywood (EW) and latewood (LW) tree rings were examined for the past 75 years (1946-2020). The results show that both EW and LW tree ring growths are primarily limited by temperature at both an upstream (Site 1) and a downstream site (Site 2), but with a tendency for precipitation becoming a growth-limiting factor at the downstream Site 2 in recent decades. This signal is stronger for LW as EW is dominated by the early snow melt period, while the LW reflects increasingly dry summer conditions. Both the δ 18O and the δ 2H values of trees close to the river fed by glacial meltwater are lower compared to those of the trees distal to the river that are reflecting snowmelt and summer precipitation but are not influenced by the glacial meltwaters draining from the upper catchment and/or released by the dam. Overall, our study suggests that tree-ring stable isotopic compositions can be used to trace changes in Alpine hydrologic regimes related to climatic changes and/or the establishments of hydroelectric regimes.