The Paris megacity has a population of 12 million residents and is among the 30 most populous cities in the world. Due to very low flow rate of the Seine River (the median Seine River flow within the Paris city limits 350 m3/s) leading to a very limited dilution factor, the Seine River basin is exposed to strong anthropogenic pressures and is considered as representative of river basins exposed to the impacts of intense human activity. Different approaches were conducted to assess the impact of the Paris Megacity on the Seine River quality as regard a large broad of organic pollutants (PAHs, PBDEs, PCBs, Phthalates or Alkylphenols). This presentation will present and discuss results of these different approaches (longitudinal profiles, annual monitoring at different stations up and downstream of Paris, pollutant loads assessment).