While rivers are widely recognized as a major vector of plastic pollution into lakes and oceans, the transport and fate of macroplastics (pieces > 5mm) and microplastics (particles < 5mm) is poorly understood at a river network scale. This collaborative project investigated the impact of stream hydrology and hydrologic variability on the transport and fate of plastic debris using three watersheds of variable sizes in North America. Within each watershed, we quantified and characterized plastic debris at baseflow, before and after storms, and during storms from four nested locations. Here, we share data from the urbanized Don River (Toronto, Canada). Our results suggest that storm events mobilize plastic temporarily stored on the riverbed or nearby terrestrial landscape into the water column, which may increase the risk of plastic exposure to river biota. The data will be used to calibrate models of plastic dynamics in rivers to better understand how climate variability will influence plastic inputs and fluxes into oceans and larger lakes.