The technique of diffusive gradient in thin film (DGT) developed by Zhang and Davison, is now commonly used to measure in situ labile metals, metalloids and phosphates in water. It has proved to be useful on account of its simplicity and wide applicability. In natural waters, formation of biofilms at the surface of the samplers is a consequence of the exposure. Biofilm growth at the surface of the samplers may affect the thickness of the diffusion layer, and/or modify the diffusion coefficient. Although biofilms may affect estimation of labile concentrations by DGT, very few studies have investigated their effect. In most cases, biofilms are not taken into account or they are considered to be insignificant. In a previous study, effect of the biofilm coming from raw waste water on DGT measurement has been investigated. A considerable impact of the biofilm on the quantification of metals has been observed. Indeed, extreme conditions were chosen to simulate a worst case of biofilm formation during deployment to facilitate the study of the effect. This new study focuses on biofouling occuring in freshwater. DGTs were deployed during 3 weeks in the Seine river. Accumulation kinetics of Cd, Cr, Co, Cu, Mn, Ni, Pb and Zn in the chelex resin were followed. In parallel, DGTs freshly assembled were deployed and removed after 5 to 7 days all along the 3 weeks of deployment in order to compare accumulation in the “fresh” DGTs and in the biofouled DGTs. accumulation in the biofouled DGTs was clearly slower than in the fresh one for all metals except Cu. Effect of biofouling on the labile concentration measured has been quantified. Compared to the raw wastewater, biofouling impact in freshwater is slightly less pronounced (for Ni, Cd, Pb) but still exists for all metals except Cu. It confirms that physico-chemical interactions between metals and the biofilm, which might be different depending on the environment where the biofilm develops, influence metal diffusion in the DGT and consequently the labile concentration measured.