n this report, we propose a tiered approach for the exposure assessment of aquatic organisms in Dutch surface waters. The tiered approach has been developed for upwards and sideways spraying techniques. The tiered approach consists of three tiers and a pre-assessment tier. In anticipation of the acceptance of the repaired FOCUS surface water scenarios in the risk assessment of active substances by the EU, the (repaired) FOCUS surface water scenario (FOCUS SW D3) is used in Tier-1. Currently, a decision on the temporal percentile to be used in the risk assessment still needs to be taken by the European Commission. Once this decision is taken and the software tools are accepted, we expect that the repaired FOCUS surface water scenarios will be adopted for use in the EU risk assessment. The concentrations calculated for the selected scenario (FOCUS SW D3) can then be used in the Dutch procedure. To guarantee consistency of the tiered approach, an assessment factor of 1.2 is proposed for Tier-1 simulations when performing an exposure assessment for surface water adjacent to large fruit crops. For avenue trees and for small fruit, an assessment factor is not necessary. The tiered approach proposed in this report is only valid for surface water concentrations and for spray applications. ; In dit rapport wordt een voorstel gedaan voor een getrapte benadering voor de beoordeling van de blootstelling van waterorganismen aan gewasbeschermingsmiddelen in oppervlaktewateren in Nederland. Deze getrapte benadering is ontwikkeld voor op- en zijwaartse spuittechnieken. De betrapte benadering bestaat uit drie trappen en een pre-beoordelingstrap. Het (gerepareerde) FOCUS oppervlaktewater scenario (FOCUS SW D3) vormt de eerste trap (Tier-1). Naar verwachting zullen de gerepareerde FOCUS-oppervlaktewater scenario’s binnenkort onderdeel worden van EU beoordeling van actieve stoffen. De Europese commissie moet nog een besluit nemen over welk temporeel percentiel moet worden gebruikt in de risicobeoordeling. Daarna en na acceptatie ...