To date, most research into the impact of microplastics in the environment has focussed on marine (coastal and ocean) environments. However, there is growing acceptance that microplastics are also pervasive within freshwater (river and lake) systems. The limited number of studies from rivers around the world have all found microplastics to be present within samples of river bed sediments or the water column. This is of concern as the ecotoxicological impact of microplastics will likely have a negative impact on a range of freshwater species with an additional public health concern if pollutants associated with microplastics then enter the human food chain. A fundamental issue regarding the science of microplastics in freshwaters is a lack of data with which to generate physically based models. This thus makes it very hard to establish what are 'normal' levels of microplastics within our rivers and hence whether such levels represent an acceptable level of risk to ecosystems or society more generally, or where clean-up or remediation strategies should be targeted. To make meaningful progress, this issue requires international consensus to be agreed quickly so that ongoing and future research efforts can be properly synthesised to provide meaningful evidence-based policy. The purpose of this proposal is to meet this challenge by assembling a new network of internationally leading freshwater microplastics experts. This network will undertake a focused programme of data collection. By pooling this data and using it to generate new numerical models at a series of workshops the network will be able to reach more robust conclusions as to the overall freshwater plastic flux to the oceans. This will address the significant stumbling block the discipline currently faces and thus allow further development of more physically based models. Such a significant deliverable can only be achieved by the sort of networking opportunity that is facilitated by the global partnerships seedcorn fund.