Rivers are an important transport route of anthropogenic litter from inland sources toward the sea. A citizen science approach was used to evaluate the litter pollution of rivers in Germany: schoolchildren within the project “Plastic Pirates” observed floating macrolitter at 282 sites and took meso-/microplastic samples (i.e. particles 1 mm - 25 mm) at over 164 sites across the entire country during the years 2016 and 2017. Floating macrolitter quantities ranged from 0 to 8.25 items m -1 h -1 (average of 0.34 ± 0.89 litter items m -1 h -1 ) and floating macrolitter was sighted at 54% of sampling sites. The quantities of floating meso-/microplastics ranged from 0 to 220 particles h -1 (average of 6.86 ± 24.11 meso-/microplastics h -1 ). They were present at 57% of the sampling sites. Given that only particles > 1 mm were sampled and analyzed, the pollution of rivers in Germany by microplastics is likely a ubiquitous problem, regardless of the size of the river. We identified six plastic pollution hotspots where 60% of all meso-/microplastics collected in the present study were found. The composition of the particles at these hotspots indicates plastic producers and possibly the construction industry and wastewater treatment plants as point sources. An identification of litter hotspots would enable specific mitigation measures, adapted to the respective source, and thereby prevent the release of large quantities of small plastic particles in rivers. The adopted large-scale citizen science approach was especially suitable to detect pollution hotspots by sampling a variety of rivers, large and small, and enabled a national overview of litter pollution in German rivers.