A growing number of studies focusing on microplastics (plastic particles smaller than 5 mm) show this issue affects all environmental matrices and compartments, and suspicions grow as to their toxicity. In this context, the Commission Internationale pour la Protection des Eaux du Léman (CIPEL) has mandated EPFL's Central Environmental Laboratory (GR-CEL) for an exploratory study on twelve benthic sediment samples from Lake Geneva. Samples have been sieved in 3 size classes (> 300 µm, > 1 mm, > 5 mm), plastic particles have been visually identified, extracted, counted and weighted, and part of them has been identified through infrared (FT-IR ATR) spectroscopy. Plastic particles have been found in all samples, most of them coming from the degradation and fragmentation of larger objects and especially plastic bags or coatings. Most of the analysed particles showed to be made of PET, PE and PVC. These exploratory results suggest further similar analysis on other samples would be appropriate, on a larger scale as well as on smaller size fractions.