Microplastics are pervasive in aquatic environments, yet their ecological impacts on small macroinvertebrates remain poorly understood. Standardized methods for quantifying microplastics in beach-cast wrack are lacking, despite its role as a natural trap for these particles. This study optimizes a cost-effective and reproducible density separation method for extracting microplastics from wrack. To assess recovery efficiency, three extraction methods were tested using polypropylene fragments and fibres. Wrack samples were collected from dry beach sections in southern Victoria using a quadrat-based approach. Microplastics were separated via NaCl-based density flotation, filtered (0.45 μm cellulose nitrate), and analysed with stereomicroscopy (Nikon SMZ800N) and NIS-Elements D software. Morphometric analysis assessed particle size, intensity, and colour, detecting microplastics as small as 0.5 μm—enhancing sensitivity beyond previous methods. Most particles were <300 µm, a size fraction often underrepresented in studies. The average microplastic density was 1.12 particles per gram of dry wrack, with fibres comprising 80% of the total and black being the most common colour (37%). This optimized protocol enhances microplastic detection in wrack, supporting more accurate contamination assessments and informing ecological impact studies.