Four perfluoroalkyl substances (PFAS) were analyzed in 62 duplicate surface water samples from the Rhône River and Marseille Bay (France; NW Mediterranean Sea). Perfluorooctane sulfonate (PFOS) was detected in all samples and exceeded the European Environmental Quality Standard (EQS) values in over 80% of the cases. The most contaminated samples were from the Rhône River (up to 200 ng L-1 ∑ 4 PFAS), as well as those collected near a wastewater treatment plant outlet in Marseille Bay (up to 9 ng L −1 ∑ 4 PFAS). While PFOS was the predominant PFAS in Marseille Bay, remarkably high concentrations of perfluorohexanoic acid (PFHxA) were measured in the Rhône River (8-193 ng L −1). The relative abundances of individual compounds differed thus significantly between the Rhône River and Marseille Bay, indicating different sources. A simulation made with the MARS3D model showed that PFOS inputs from the Rhône River can enter Marseille Bay at levels > EQS.