Microplastics (MPs; 1 µm to 5 mm) have been widely reported in freshwater environments. We applied a systematic quantitative literature review approach to analyse 183 studies reporting MPs in freshwater. The concentrations of MPs in various freshwater environments globally spanned up to eight orders of magnitude in water (1.2 × 10⁻³ to 5.42 × 10⁵ particles/m³) and six orders of magnitude in sediments (8.1 × 10⁻¹ to 9.5 × 10⁵ particles/kg). However, the methods used to extract and analyse MPs varied greatly across studies, which led to inconsistency in the reported results and hindered the comparability between studies. Despite an increasing number of studies published in recent years on MPs in freshwater, there are still significant knowledge gaps. First, little is known about the presence of MPs in constructed wetland, a key component treating stormwater and wastewater. Second, information about smaller MPs (1-20 µm) is often missing due to technical limitations in sampling and detecting such small particles. Last but not least, the lack of comprehensive quality assurance and quality control (QA/QC) measures in the literature, especially inclusion of field blanks and positive controls, made the results less reliable. Based on the findings of our review, this study aims to quantify and characterise MPs in water and sediment of five constructed wetlands across Queensland with different land uses and source of inflow (i.e., wastewater and stormwater). Triplicates water and sediment samples will be collected from both inlet and outlet of the selected sites, and MPs will be identified using Fourier transform infrared spectroscopy FTIR (>25 µm) and Raman spectroscopy (1-25 µm). Additionally, a comprehensive QA/QC protocol will be implemented, including field and laboratory blanks and positive controls to ensure the quality of data. The results provide an understanding of MP contamination, especially for smaller MPs, in constructed wetlands.