The occurrence of microplastics in the aquatic ecosystems, especially in the oceans, is a matter of public record. It is estimated that about 80% of microplastic particles found in oceans and seas are discharged via rivers. But on many rivers especially in Poland, there are dam-reservoirs. The authors wanted to research the role of dam-reservoirs in microplastic removal from the watercourse in this study. The research was done on three rivers were dam-reservoirs are localized. Samples of suspended matter (containing microplastic particles) were taken upstream of the reservoir and as near as possible under the dam. Results showed that the majority of plastic particles are accumulated in the area of the lake, but the presence of microplastics in samples taken under the dam points to the processes that microplastics are transported to the lower parts of the water column.