High alpine catchments are affected by climate change, but have not been studied as intensely as other ecosystems. This Master's thesis aims at the detection of long-term trends in the ecohydrology of the Macun lake system. This catchment is located in the Swiss National Park and consists of two basins with different water sources. The data analysed consists of three major parts: yearly sampling of 10 sites since 2002 and sampling over the snow-free period of 2002 and 2017 of 31 sites. During each sampling campaign, a water sample was collected for later lab analysis and temperature, conductivity, and turbidity were measured in the field. Additionally, there are data available from an Exosonde located near the outlet of Lai d'Immez, which recorded data from summer 2016 till early spring 2017 and summer 2017 until present. Over the past 17 years, DN and TIC showed the strongest changes. DN decreased while TIC increased, which corresponds to atmospheric concentrations. Further, pH dropped and is now below 6, which seems to affect diatom communities. Both years, 2002 and 2017, showed spatial differences, but a decrease in those differences was not detectable. During the snow-free period in 2017, both spatial and temporal differences were present. The southern, glacialy influenced basin, showed higher variation than the north basin. Conductivity and nitrogen had higher concentrations in the south basin, which is due to the glacial input. The north basin on the other hand had higher concentrations of organic carbon, which indicates a higher productivity of this basin. This thesis has identified various trends and patterns, and offers a basis for further research in the same catchment as well as for comparison with other catchments.