We measured floating plastic and other anthropogenic litter at 26 measurement locations distributed across the Dutch reaches of the Rhine (IJssel, Waal, Nederrijn) and Meuse rivers (see Figure 1) between 28 January and 7 December, 2021. The Rhine enters the Netherlands from Germany at Spijk, and splits into the main Waal, IJssel and Nederrijn. The Waal is the main branch, and joins the Nederrijn-Lek branch at Rotterdam before flowing into the North Sea. The IJssel flows into Lake IJssel at Kampen. The Meuse enters the Netherlands from Belgium at Eijsden, and discharging into the tidal Hollands Diep estuary. Here, the Meuse is joined by a Rhine distributary before reaching the North Sea. Floating macroplastic and macrolitter (>0.5 cm) were measured using the visual counting method, for which all items floating at the surface are counted from bridges. Only bridges that are safe and legally accessible, e.g. presence of pedestrian or bicycle paths, were selected. At each location, three to twelve observation ...