Mapping the Impact of River Plastic Interception Across River–Coast Systems

Rivers are major pathways for transporting land-based plastic pollution to the ocean, with much of this material accumulating along nearby coastlines. To address this issue, The Ocean Cleanup deploys river interception systems worldwide to halt plastics before they reach the sea. However, the extent to which river interception reduces coastal pollution has not yet been empirically demonstrated. In this study, we introduce a standardized impact‑mapping approach that integrates (i) baseline assessments of beached plastic composition, (ii) quarterly beach monitoring, and (iii) biannual characterization of intercepted riverine plastics following the deployment of interception technologies. Using the first year of data from two pilot locations – the Motagua River (Guatemala) and the Klang River (Malaysia) – we show that plastic composition exhibits substantial spatial and temporal variability in both riverine and coastal environments. Moreover, periods of elevated riverine plastic flux correspond to increased concentrations of beached plastics. Item‑level characteristics – including country of origin, age, and degradation state – provide additional insight into whether stranded plastics stem predominantly from local terrestrial inputs or from longer‑residence marine sources. As we expand this program to several further global locations, these results will support improved calibration of river‑to‑coast transport models and strengthen our ability to quantify and evaluate the coastal pollution impact of The Ocean Cleanup’s river interception technologies.