This dataset corresponds to a data series produced from automated data loggers during the MESOLAC experimental project. In July 2019 we deployed nine pelagic mesocosms (about 3000 l, 3m depth) in Lake Geneva near the shore of Thonon le Bains, France, to simulate predicted climate scenarios (i.e. extreme events) and assess the response of pelagic communities, ecosystems functioning and resilience. The experiment lasted 4 weeks (July 4 – 30, 2019) and the design consisted of three treatments each replicated 3 times: a control treatment (no treatment applied – named C) and two different treatments simulating extreme weather events. The high intensity treatment (named H), aimed at reproducing short and intense weather events such as violent storms. It consisted of a short-term intense stress applied during the first week, with high pulse of dissolved organic carbon (5x increased concentration), light reduction up the 95% and water column manual mixing. The medium intensity treatment (named M), simulated less intense and more prolonged exposures such as during flood events. It was maintained during the 4 weeks and consisted of 1.5x increased concentration of dissolved organic carbon, light reduction up to 70 % and water column manual mixing. During the experiment, automated data loggers were placed in the mesocosms at different depths for continuous environmental monitoring of temperature, dissolved oxygen and CO2. Here these data are presented in the dataset file, ordered by treatment (Control, High and Medium) and replicates. For each time point the measured parameters are listed in columns, a summary table of all the measures is provided as well in the excel dataset file.