Understanding the thermal behavior of lakes is crucial for water quality management. Under climate change, lakes are warming and undergoing alterations in their thermal structure, including surface water and deepwater temperatures. These changes require continuous monitoring due to the possible major ecological implications for water quality and lake processes. We combined numerical modeling and satellite thermal data to create a regional dataset (LakeTSim: Lake Temperature Simulations) of long-term water temperatures for 401 French lakes in order to tackle the scarcity of in situ water temperature (Sharaf et al., 2023; https://doi.org/10.57745/OF9WXR). The dataset consists of daily epilimnion and hypolimnion water temperatures for the period 1959-2020 simulated with the semi-empirical OKPLM (Ottosson-Kettle-Prats Lake Model) and the associated uncertainties. Here, we describe the model and its performance. Additionally, we present an uncertainty analysis of simulations with default parameter values (parameterized as a function of lake characteristics) and calibrated parameter values along with the analysis of the sensitivity of the model to parameter values and biases in the input data. Overall, the 90 % confidence uncertainty range is largest for hypolimnion temperature simulations, with medians of 8.5 and 2.32 • C, respectively, with default and calibrated parameter values. There is less uncertainty associated with epilimnion temperature simulations, with medians of 5.42 and 1.85 • C, respectively, before and after parameter calibration. This dataset provides over 6 decades of epilimnion and hypolimnion temperature data crucial for climate change studies at a regional scale. It will help provide insight into the thermal functioning of French lakes and can be used to help decision-making and stakeholders.