Microplastics (MPs) have emerged as an important scientific issue of global concern and have been extensively reported in each environmental compartment, with aquatic environments regarded as the ultimate receptors and sinks. Identifying relevant pathways through which MPs reach freshwater systems is difficult due to the complex and interconnected nature of the activities involved in generating plastic waste. Nevertheless, most studies have consistently reported wastewater treatment plants (WWTPs) as an important pathway through which MPs reach surface waters. However, recent studies have exposed other important routes, particularly stormwater runoff, atmospheric deposition, agricultural inputs, and littering. Despite the efforts to highlight the key routes of MP contamination, the relative importance of these pathways is likely to vary geographically and temporally, influenced by various factors that collectively hinder our ability to develop practical and effective management policies. Therefore, to address the pervasive issue of MP pollution in freshwater systems, the first step is to comprehensively summarize the critical pathways to fully understand how MPs enter and disperse in these systems. Future research should explore these questions, which could help allocate resources more effectively by first targeting the most significant pathway. In addition, we need standardized methods to quantify and analyze MPs across different pathways. To this end, this chapter addresses these questions specifically in the context of freshwater ecosystems, providing key insights into sustainable MP management.