Diffusive gradient in thin films (DGT) have been widely used to measure cationic trace metals such as lead, cadmium or nickel in surface waters. However, DGT based on a polyacrylamide diffusive gel and a Chelex resin does not allow trapping methylmercury (MeHg) and inorganic mercury (HgII). Consequently, it was recommended to use agarose as diffusive gel. The most common resins used for MeHg and HgII measurements are the spheron-thiol resin and the 3-mercaptopropyl functionalized silica gel (3M) combining a thiol function and a Si group. Some in situ measurements were carried out with both type of DGT but mainly in contaminated rivers (HgTD>20 ng/L). Until now, few studies have focused their work on the application in freshwaters of a DGT based on 3M resin combined either with a diffusive gel in agarose or in polyacrylamide. Moreover, these studies were carried out in surface waters with high Hg (HgTD>5 ng/L) or MeHg (MeHgTD=0.27-0.34 ng/L) concentrations. The aim of this study was to assess in situ MeHg concentrations in low contaminated surface waters by using a home-made agarose/3M DGT. Thus we developed an adapted method allowing the extraction, derivatization and the quantification of the mass of MeHg trapped by the home made/3M DGT at environmental levels. Therefore, we focused our work on the control of Hg contamination mainly via the control of blank DGT, which could influence the estimated concentrations of total mercury (HgTOT) and MeHg at very low levels. Moreover, home-made/3M DGT were deployed in situ in a low-contaminated river (Bourbre River; HgTOT ~0.5 ng/L) and methods were applied to assess their relevance in environmental conditions and to assess time-weighted average (TWA) concentrations. Our home-made resins prepared in clean room conditions with reagents of high purity and a specific cleaning procedure, present low total mercury level (