Plastic debris has become a global environmental issue. Among the various sizes of plastic debris, microplastics (plastic particles less than 5 mm) have attracted enormous attention due to their small size and ubiquitous presence in aquatic systems worldwide. Wastewater treatment plant effluent and stormwater runoff have been identified as the main pathways of microplastics to aquatic environments. Constructed wetlands, which are used as treatment systems for wastewater and stormwater, may play a significant role in reducing the release of microplastics to receiving environments, but they are relatively understudied compared to other freshwater compartments given their functions and ecological relevance. Additionally, ingestion of microplastics has been documented in a range of non-target organisms and subsequent adverse effects have been reported, but exposure conditions have often not been environmentally realistic. The overall aim of this thesis was to 1) highlight current knowledge gaps by summarising the current state of knowledge of microplastic research in freshwater environments, 2) investigate the extent of microplastic contamination in constructed wetlands to better understand the potential role of these artificial systems in managing microplastic contamination, and 3) evaluate the effects of microplastics on common Australian freshwater organisms under environmentally relevant conditions. [...]