Background In Switzerland the assessment of surface water quality with respect to contaminations by plant protection products (PPP) is based on the Swiss water protection law (Schweizer Bundesgesetz vom 24. Januar 1991 über den Schutz der Gewässer, Gewässerschutzgesetz, GSchG, SR 814.20), as well as on the Swiss water protection ordinance (Gewässerschutzverordnung vom 28. Oktober 1998, GSchV, SR 814.201). According to GSchV a general quality criterion of 0.1 μg/l exists for single organic pesticides (plant protection products and biocidal products) in Swiss running waters. Other values remain subject to reserve on the basis of individual substance assessments in the context of the authorisation procedure. In the European Union, the protection of water bodies is regulated under the Water Framework Directive (2000/60/EC, WFD). In addition, the aquatic risk of PPP is already being assessed during the PPP authorisation procedure under the ordinance on the placing of plant protection products on the Swiss market (Verordnung vom 18. Mai 2005 über das Inverkehrbringen von Pflanzenschutzmitteln, Pflanzenschutzmittelverordnung, PSMV, SR 916.161) and in the EU under the Council Directive 91/414/EEC of 15 July 1991 concerning the placing of plant protection products on the market. [...]