Abstract: Microplastics (MPs) are found in many different environments. The aim of the present study was to quantify and map sources of MPs pollution in the Elbe River basin, which is the fourth largest river basin in Central and Western Europe. We identified the most relevant sources of MPs, including tyre wear, synthetic textile fibres, paint chips and plastic beads from cosmetics. The mapping was based on location-specific proxies, e.g., the per capita MP emissions from different sources combined with the population density of a given agglomeration. Methods were developed to include factors affecting the MP release process to produce more realistic estimates. For example, fabric type and washing temperature are both influencing the amount of microfibres released, and the amount of tyre wear particles released varies considerably from one vehicle to another when driving on different types of roads. The results of this study will be used as input for modelling the fate of MPs in the Elbe River basin. For this, we will use the “Exposure to Pharmaceuticals in the Environment” model (ePiE) which originally was developed for calculating concentrations of active pharmaceutical ingredients (APIs) in surface waters. The model will be adapted to simulate the advective transport and degradation of MPs in rivers to provide a more comprehensive understanding of the sources, fluxes, accumulation areas and fate of the MPs in rivers.