Plastic accumulation in the marine environment is a major concern given the harmful effects and longevity of plastics at sea. To understand and mitigate this accumulation, an understanding of plastic transport in rivers and estimates of riverine plastic flux are required (since rivers are potentially significant transport pathways of plastic debris to the oceans). Existing methods to investigate plastic transport in rivers and to estimate riverine plastic flux (from field measurements and

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... ing efforts) are, however, very crude, subject to a high degree of uncertainty and (perhaps most importantly) fail to consider the processes controlling displacement. Here, a new and fundamentally different approach to investigating plastic transport in rivers is presented, which considers the travel distances of individual items of macroplastic debris (and thus, the processes controlling displacement). This approach combines an experimental component, in which macroplastic tracers were tracked in a small river reach, with the construction of a numerical model, which is intended to act as an interpretive conceptual framework. Macroplastic travel distances were found to be low and variable and the travel distance distribution was systematically controlled by the location and characteristics of 'trapping points' (particularly overhanging trees and meander bends). The numerical model was based on 'the probability of trapping' and described particle displacement distributions reasonably well. Although significant knowledge gaps remain (which require further investigation), the tracer experiment results and outputs from the numerical model demonstrated the feasibility of using a travel distance approach to understand and predict plastic transfer in rivers. This approach also has the potential to improve riverine plastic flux estimates.