Rivers influence the density, composition, form, and transport of plastic litter to downstream ecosystems. Stormwater is a source of plastic pollution into waterways and a primary driver of plastic export. However, few studies have quantified plastic litter composition before, during, and after storms throughout a river continuum. In addition, because this is a newly emerging field, combining field and laboratory approaches that span multiple particle sizes is uncommon (i.e., microplastics <5 mm and macroplastics > 5 mm). We measured standing stocks of microplastics (floating, water column, and benthic) and macroplastics (riparian, floating, and benthic) before and after individual storm events at 3 sites in an urban watershed (Chicago River, USA). We predict total standing stocks of micro- and macroplastics will be similar before and after storms because storms re-suspend and transport plastics downstream, but also input new plastics to the sites. Also, we predict the composition of benthic plastics (i.e., color, size, shape, and polymer types) could be different before and after storms, illustrating a change in the plastic 'community', despite similar overall abundance of particles. During storms, we expect a hysteresis in water column plastic concentration, where rising limbs are associated with the highest concentrations of plastic particles relative to other components of the hydrograph. These data are critical to quantify plastic dynamics in urban streams and inform new models of watershed plastic dynamics.