This paper discusses the opportunities and constraints regarding the effective implementation of the European Water Framework Directive (WFD) in the area of diffuse nitrate pollution. Owing to the subsidiarity principle and a new procedural mode of governance, the WFD only sets distinct environmental targets, leaving most decisions on how to operationalize and institutionalize the reduction of diffuse nitrate pollution to the member states. This is a particular challenge for Germany, where lower scale regions have become the main implementers of European water policy. Successful implementation of the WFD, i.e. the actual improvement of water quality, depends on a series of key contextual and contingent factors, operating at a regional scale. In a Northwest German region with intensive agriculture and severe nitrate pollution, we analyse the historical and economic context and actor network of the region as well as the influence of environmental groups on public participation, the potential of biogas technology and new financial options. Besides the specific influence of these factors on the implementation process, we explore the uncertainties and difficulties surrounding European legislation and its operationalization in Germany and on a regional scale. Copyright © 2007 John Wiley & Sons, Ltd and ERP Environment.