The presented dataset is composed of high frequency sensors data, vertical in situ profiles and laboratory chemical analysis data, acquired during an aquatic mesocosm project simulating terrestrial organic matter transfers to lake food web. The DOMLAC experiment was located at the OLA (“Long-term observation and experimentation for lake ecosystems”) facility at the UMR CARRTEL in Thonon les Bains, on the French shore of Lake Geneva. It consisted of nine inland mesocosms (2.1 m length, 2.1 m width and 1.1 m depth) with a total volume of approximately 4000 L and filled with water directly supplied from the lake at 4m depth. The experiment lasted 3 weeks (4-21 October 2021) and aimed to simulate predicted climate scenarios (i.e. extreme events such as storms and floods) by reproducing changes in quality and composition of lake subsidies and runoff by increased inputs of terrestrial organic matter. The design of the experiment included three treatments each replicated three times: a control treatment (no treatment applied) and two treatments simulating allochthonous inputs from two different dissolved organic matter (DOM) extract from peat moss (Peat-Moss treatment) and phragmites (Phragmite treatment). The dataset is composed of: 1. In situ measurements from automated data loggers of temperature, conductivity, dissolved oxygen and CO2 acquired every 5 minutes at 0.1, 0.5 and 1 m depth for the entire period of the experiment. 2. In situ profiles (0-1 m) of temperature, conductivity, pH, dissolved oxygen (concentration and saturation) acquired twice a week during the experiment. 3. In situ measurements of light spectral UV/VIS/IR irradiance (300-950 nm wavelength range) taken at 0, 0.5 and 1 m twice a week on the same day of the profiles at point 2. 4. Laboratory chemical analysis of conductivity, pH, total alkalinity, NH4, NO2, NO3, total and particulate nitrogen (Ntot, Npart), PO4, total and particulate phosphorus (Ptot, Ppart), total, particulate and dissolved organic carbon (TOC, POC, DOC), Ca, K, Mg, Na, Cl, SO4 and SiO2 of integrated samples taken twice a week on the same day of the in situ profiles at point 2 and 3. 5. Laboratory analysis of pigments (Chla, Chlc, carotenoids, phaeopigments) extracted from samples collected at point 4. 6. Specific absorbance on the range 600-200nm of DOM (i.e. <0.7 µm) measured on samples collected at point 4.