The consequences of lake level regulation on riparian forests have been little investigated in Europe, although they shelter a wide variety of habitats and species and are threatened in most European countries. This study therefore aims to improve our understanding of the past and future dynamics of wetland forests in Central Europe. Historical plant surveys (conducted around 1980) were compared with more recent surveys (2020) at the same locations in the Grande Cariçaie reserves, along the Lake Neuchâtel (Switzerland), regulated since 1962. The inventories were clustered into plant communities, and floristic diversities were compared. Changes in environmental conditions were evaluated using ecological indicator values. The species composition in tree and shrub layers was compared to predict the potential future evolution of these forests. Four types of forest communities have been identified and denoted as the Alnus glutinosa, A. incana, Fraxinus excelsior and Pinus sylvestris groups. Over the course of 40 years, some sites shifted between communities, particularly from the wet A. incana group to the drier F. excelsior group. We noticed a loss of hygrophilous and heliophilous species. Moreover, the regeneration of the dominant tree species is very low in the A. glutinosa and F. excelsior groups, and even absent in the P. sylvestris group. The riparian forests on the shores of the regulated lake are losing their characteristics, with significant changes in species composition. Over 40 years, the conditions have become drier, the canopy density has increased, and the understorey has suffered from shadier conditions, resulting in a loss of diversity at the landscape scale. The drier conditions are probably mainly following the lake regulation (lower variations of water level), but increasing evapotranspiration due to climate change cannot be excluded.