Plastics in freshwater is of increasing concern to the public, given its potential negative impact on socio-ecological systems. At the same time, plastic monitoring is a rather fresh topic in the field of water quality monitoring, and there hardly exist any globally applicable standards for monitoring plastics in freshwaters on a global scale. Against this background, UN Environment and the Helmholtz-Centre for Environmental Research (UFZ) aim at providing harmonized monitoring methodologies of macro-plastics and microplastics in rivers and lakes. The ultimate goal is to reduce and prevent marine litter and microplastics pollution from rivers in the future. The implementation of such guidelines depends, however, on the goals and capacities of States with regards to water quality monitoring. The project ‘Monitoring Plastics in Freshwaters – A Participatory Approach’ supports the goals of UN Environment and UFZ, by organizing the involvement of stakeholders into the development of recommendations for plastic monitoring. This includes three consecutive steps: (i) an initial understanding of the respective stakeholder landscape via stakeholder analysis, (ii) a better understanding of the goals and capacities of plastic monitoring via the design and circulation of a survey amongst these stakeholders, as well as (iii) a qualitative feedback process via virtual workshops. The results of this participatory approach shall be presented at international events and published within the monitoring guidelines of UN Environment and in the scientific community. Moreover, avenues for future research shall be identified to better place the citizens’ needs into the monitoring process in the future.