Data from OLA, Observatory of Lakes (http://www6.inra.fr/soere-ola, ©SOERE OLA-IS, AnaEE-France, INRA Thonon-les-Bains, CISALB, CIPEL, SILA, developed by Eco-Informatics ORE INRA Team). The data acquisition surveys were performed in 2016, in France, on Lakes Annecy (45°51’24’’N; 06°10’20’’E) and Bourget (45°43’55’’N; 5°52’06’’) from September 12th to 15th and 26th to 30th, respectively. The hydroacoustic data were collected at 38, 70 and 200 kHz using Simrad echo sounders (EK60, ER60) and transducers (ES38-7B, ES70-7C and ES200-7C). The transducers were set in a frame to beam vertically, as close as possible to maximize sampling volume overlap. The frame was pole mounted on the vessel. The transducers were immerged to 0.70 m depth. Pulse lengths were set to 0.256 ms (Godlewska et al., 2011) and transmitted at 5 Hz with a transmitting power of 100 W. Calibration was performed for all frequencies according to the standard protocol of Foote et al. (1987) and the manufacturer manual before survey in both lakes. Calibration results agreed well with previous tank calibrations at Ifremer (Brest). The surveys were performed in calm to moderate wind conditions at a speed of about 8 km.h-1 using zig-zag (Lake Bourget survey) and parallel transects (Lake Annecy survey) designs.