This dataset corresponds to the physico-chemical parameters data series produced during the MESOLAC experimental project. The presented dataset is composed of: 1. In situ profiles (0-3m) of temperature, conductivitivy, pH, oxygen (concentration et saturation). 2. In situ measures of light spectral UV/VIS/IR irradiance (300-950 nm wavelength range) taken at 0, 0.25, 0.5, 1, 1.5, 2 and 2.5m. 3. Laboratory chemical analysis of samples collected at 0 and 2 m (conductivity, pH, total alkalinity, NH4, NO2, NO3, Ntot, Npart, PO4, Ptot, Ppart, Ctot, Cpart-org, Cpart-tot, Cl, SO4, SiO2). 4. Laboratory analysis of pigments extracted from samples collected at 0 and 2 m (Chla, Chlc, carotenoids, phaeopigments). The experiment consisted of nine pelagic mesocosms (about 3000 L, 3m depth) deployed in July 2019 in Lake Geneva near the shore of Thonon les Bains, France, to simulate predicted climate scenarios (i.e. extreme events) and assess the response of pelagic communities, ecosystem functioning and resilience. The experiment lasted 4 weeks (July 4 – 30, 2019) and the design included three treatments each replicated 3 times: a control treatment (no treatment applied – named C) and two different treatments simulating extreme weather events of different intensities. 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 (DOC 5x increased concentration compared to the control), light reduction up the 95% and water column manual mixing daily for 15 mins. 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 DOC compared to the control, light reduction up to 70 % and water column manual mixing daily for 5 mins. During the experiment, physical parameters were measured twice a week and samples were collected at the same date at the depth of 0 and 2m for subsequent chemical laboratory analyses. These data are presented in the dataset file, ordered by sampling event (numbered from S1 to S8), treatment (Control-C, High-H and Medium-M) and replicates (1 to 3). For each time point the measured parameters are listed in columns, missing data are marked as NA.