The European Directive 2000/60/CE delineates the objectives of a good ecological and chemical status for rivers to achieve before 2015. The present project focuses on a pond-reservoir system (later referred to as a constructed wetland, CW), which can be used as a buffering system to lower the impact of agricultural practices on hydrosystems and decrease or limit the transfer of contaminants flowing toward surface waters. The CW studied is located at Aulnoy, 70 km northeast of Paris (France). The aim was to assess the efficiency of a CW in terms of nitrate removal and analyze the hydrological balance of the CW and the agricultural catchment. This study showed potential nitrate removal based on a decrease in average nitrate contents measured over a period of 8 years between the inlet and the outlet of the CW. Average values of 12.6 14 and 6.4 mg N–NO3/L, respectively, were measured at the main drain, the spring and the reservoir; this led to a 50 _ 18% (mean _ standard deviation) reduction of nitrate fluxes. The semi-potential denitrification experiments confirmed the denitrification capacity of CW sediments. Conclusively, this CW can treat waters from agricultural drainage, producing outflow quality in line with the expectations of a good ecological status as defined by the European Directive 2000/60/CE.