Abstract: Several millions of tons of macroplastics are annually transported by rivers across large distances while releasing micro- and nanoplastics and other hazardous substances into ecosystems, which ultimately result in environmental and human exposure. Plastics can readily be found in the river floodplains, in suspension in the flow, buried within sediments or entrapped in vegetation. Either in the air or in water, plastics are transported through different multiphysics mechanisms which, oftentimes, resemble those assimilated by hydraulic engineers for other matter such as sediments or bubbles. In this seminar, we expand on how existing and new fluid mechanics knowledge can be tailored and applied to assist a wider community of plastic scientists to tackle this wicked problem. The focus is put on recent work conducted in laboratory using positively and negatively buoyant macroplastics. In our experiments, we tracked roughly 7,500 plastics in 3D at millimeter to sub-millimeter accuracy, subject to river-like flows. This data is used to unwrap detailed plastic mechanisms defining their transport. In this seminar, we will also show how this knowledge is relevant to develop robust monitoring campaigns, improve cleanup efforts, or assist in the prediction of plastics fate through the environment.