Research into microplastics is increasingly important, as these particles are widespread and their long-term effects remain unclear. Plastic waste enters rivers and breaks down into smaller fragments, prompting our focus on mesoplastics in rivers—an under-researched area. Based on litter collection efforts along the Danube, we selected sampling sites near Komárom, Almásfüzitő, Dunaalmás, and Neszmély. Data from these “clean-up” actions were used to assess anthropogenic inputs and to conduct both quantitative and qualitative analyses. During the river sampling methods, where the goal was to develop a method suitable for domestic conditions, custom-made nets were applied based on descriptions found in the literature. The size, quantity, and polymer type of the particles were determined through visual inspection and FTIR spectroscopy. According to our test results so far, most of the particles were identified as originating from packaging waste, mainly polyethylene and polypropylene. The highest contamination was measured 20 m from the shore of Almásfüzitő, close to the drift line, concentrated in the upper 20–50 cm layer of the river water, which correlates with the results found in the literature regarding water depth. Based on these findings, it can be concluded that our measurement method, which is still under development, is progressing in the right direction, but further measurements will be required to confirm this with greater certainty.