Lake Toba, located in the Bukit Barisan Mountain range, is the largest volcanic lake in Southeast Asia and the world. It was formed by an ancient supervolcanic eruption approximately 75,000 years ago. The lake is surrounded by densely populated areas and fed by 289 inflowing rivers, making it highly vulnerable to microplastic contamination from various anthropogenic sources. Water and sediment samples were collected across 15 water stations and 4 sediment stations, positioned based on a preliminary macroplastic assessment using Sentinel-2 remote sensing analysis. However, information regarding the presence of microplastics in volcanic lake environments remains limited. Water sampling was conducted using a plankton net, while sediment samples were collected using a sediment trap, followed by drying and observation under a stereo microscope; polymer identification was performed using Fourier Transform Infrared (FTIR) spectroscopy. The results revealed that the dominant microplastic shape in the lake water was pellets, characterized by a yellow coloration and a size of < 325 μm. The highest microplastic concentration was recorded at Station 4 with 108 particles/L, whereas the lowest concentrations were observed at Stations 2 and 8 with 10 particles/L. FTIR analysis indicated that polypropylene (PP) was the most dominant polymer type (22.2%), likely originating from packaging and textile waste, while polyvinyl chloride (PVC) and cellulose acetate (CA) exhibited the lowest proportions at 3.7% each. The widespread occurrence of microplastics demonstrates a significant anthropogenic impact on the aquatic ecosystem of Lake Toba and highlights potential ecological risks to aquatic organisms and surrounding communities. These findings provide critical baseline scientific data for environmental monitoring, sustainable lake management, and the development of mitigation strategies for microplastic pollution in the Bukit Barisan region.