Riparian zones are located at the interface between terrestrial and fluvial ecosystems; and thus, they are particularly vulnerable to plastic pollution. Mismanaged plastic can reach riparian zones from local inputs of adjacent urban, industrial or agricultural areas. In addition, during high flow conditions or episodic floods, plastic can be flushed from riparian zones into the stream and transported downstream, where in turn, it can be trapped into riparian zones, especially in the presence of vegetation. Therefore, abundance of plastic in a riparian zone can result from the interplay between local human activity and the net effect of stream hydrologic dynamics. In this study, we assessed the degree of plastic pollution (i.e., abundance and category type of the fraction >5 mm, macroplastic-MacP) in the riparian zones of a Mediterranean stream, and examined how it is affected by the catchment land use and the stream hydrological regime. Thirteen sites spanning forested, agricultural, and urban areas were surveyed for MacP abundance on a single date in the riparian zone and stream channel. Additionally, five sites were sampled bimonthly to assess temporal variation of MacP abundance. MacP was mostly found in riparian zones (67%) rather than in the stream channel (<15%). Indicating that riparian zones are hot spots of plastic accumulation. Abundance of MacP was higher in riparian zones nearby urban areas than nearby forested and agricultural areas. This evidences the different influence of human activities on plastic pollution in riparian zones. Floods cause a distinct effect on riparian MacP abundance among riparian zones, which was mostly associated with the vegetative structure of these zones than with their location along the fluvial network. Together, these results shed light about some factors and mechanisms that explain how plastic pollution in catchments ultimately reaches marine ecosystems. It also provides insights on potential management strategies to help reducing plastic pollution in stream-riparian ecosystems.