In urban areas, small lakes are frequently of utmost ecological importance as they represent hotspots for biodiversity. However, they often suffer from high loads of nutrients and pollutants coming from the watershed, leading to strong eutrophication. Harmful algal blooms can occur and severely alter the ecosystem services provided by urban lakes. Among the factors triggering of algal blooms, two are essential: warm water temperature and alternation between stratification and mixing events. The aim of this study is to investigate the long-term evolution of a small lake thermal regime through the combined use of high-frequency measurements (10 min) and hydrodynamic modelling. We calibrated and validated a 3D hydrodynamic model (Delft3D FLOW) with data collected over 3 years (2016-2017). We then simulated with this model a long period of 38 years, from 1980 to 2018. Different indicators are defined to investigate the lake thermal dynamics, in terms of water temperature and stratification and in relation to biological processes (growing degree days). Based on the hindcast outcomes, the trends of these different indicators are analyzed.