Citizen science projects spring up in freshwater monitoring, with an increasing number of projects in river, lake, and groundwater monitoring around the globe. Citizen science scholars assume that these projects have different designs, including diverse characteristics of citizens, institutions, and forms of interactions, potentially affecting the outcomes of these projects. Given the strong focus on case studies or reviews in the field, there is, however, little comparative evidence of the different types of citizen science projects in freshwater monitoring. Based on a global survey, this study provides a systematic comparative analysis of the design of 85 citizen science projects in the field of freshwater monitoring. Descriptive statistics reveal how projects differ along 45 literature-based design variables raised in the survey. Factor analysis based on 31 of these variables yields ten key design factors, and cluster analysis, based on these design factors, allows to identify seven distinguished clusters of citizen science projects. While these clusters are rather heterogeneous, they reveal differences between groups of projects regarding institutional motivation, citizen characteristics, and interaction forms. These results significantly add to a systematic comparison of citizen science projects in freshwater monitoring and enable a more effective involvement of citizens in environmental management.