The main objective of the TELQUEL (TELédétection de la Qualité Ecologique des Lacs) project is to provide quantitative remotely sensed observations to monitor the ecological state of the French lakes. In this direction, MSI/Sentinel-2 and OLI/Landsat 8 data are exploited to : (i) identify/develop a specific atmospheric correction and deginting algorithm over lake areas (see Poster from Harmel, T. et al. in this conference); (ii) provide bio-optical algorithms to retrieve water transparency and water constituent concentrations (Chl-a, CDOM and TSM), first results are shown in this poster. (iii) use the retrieved bio-optical properties and matter concentrations for enhancing the lake water quality evaluation and biogeochemical models.