(Plastic) litter in aquatic ecosystems negatively impacts ecosystems, species and economic activities. Rivers play a key role in transporting land-based waste towards the ocean [1]. A large portion is retained within river basins, e.g. in the estuary, in sediments and on the riverbanks. To effectively identify litter sources, sinks and transport mechanisms, reliable data are crucial. Such data can support optimizing litter prevention mitigation and clean-up efforts. We present the results of a two-year monitoring campaign focused on riverbank macrolitter (¿0.5 cm) in the Dutch Rhine-Meuse delta. Between 2017 and 2019, volunteers sampled 152,415 litter items at 212 unique locations [2]. All items were categorized based on the River-OSPAR method (based on the OSPAR beach litter guidelines), which includes 110 specific item categories across ten parent categories. The median litter density was 2,060 items/km, and the most observed items were foam, hard, and soft plastic fragments (55.8 %). Plastic bottles, food wrappings and packaging, caps, lids and cotton swabs were the most abundant specific items. The litter density and most abundant items vary considerably between rivers, along the river, and over time. For both rivers, the highest litter density values were found at the Belgian (Meuse) and German (Rhine) borders, and at the Biesbosch National Park, the most downstream location. We provide a first scientific overview of the abundance, top item categories, and spatiotemporal variation of (plastic) litter on riverbanks in the Dutch Rhine-Meuse delta. In addition, we evaluate the used River-OSPAR method and provide suggestions for future long-term monitoring strategies. The results can be used by scientists and policy-makers for future litter monitoring, prevention and cleanup strategies. References [1] van Emmerik, T, and A Schwarz. P̈lastic debris in rivers.ẄIRE: Water (2020) [2] van Emmerik, T, et al. R̈iverbank macrolitter in the Dutch Rhine-Meuse delta.Ënvironmental Research Letters (2020), https://doi.org/10.1088/1748-9326/abb2c6