Riverine systems act as converging pathways for discarded litter within drainage basins, becoming key elements in gauging the transfer of mismanaged waste into the ocean. However, riverine litter data are scarce and biased towards microplastics, generally lacking information about larger items. Based on the first ever database of riverine floating macrolitter across Europe, we have estimated that between 307 and 925 million litter items are released annually from Europe into the ocean. The plastic fraction represented 82% of the observed litter, mainly fragments and single-use items (that is, bottles, packaging and bags). Our modelled estimates show that a major portion of the total litter loading is routed through small-sized drainage basins (<100 km2), indicating the relevance of small rivers, streams and coastal run-off. Moreover, the major contribution of high-income countries to the macrolitter inputs suggests that reducing ocean pollution cannot be achieved only by improving waste management, but also requires changing consumption habits and behaviour to curb waste generation at source. The inability of countries with well-developed recovery systems to control the leakage of waste into the environment further supports the need to regulate the production and use of plastic on a global scale. We acknowledge the additional members (coordinators and observers) of RiLON, listed in Supplementary Data 5, for their support in the field data collection and feedback during the data quality control. D.G.-F. was supported by the JRC institutional exploratory project RIMMEL (272346), PLASTREND (BBVA Foundation) and the European Union (H2020-MSCA-IF-2018 846843 - LitRivus). J.V. and C.M.-C. were supported by the MIDaS project (Spanish Ministry of Science, Innovation and Universities, CTM2016-77106-R, AEI/FEDER/UE). Peer reviewed