This study investigates the sources of microplastics (MPs) in Beijing's urban water bodies, including rivers, lakes, and suburban sewage. MPs are challenging to trace due to their complex transportability. The research combines MP diversity with a conditional fragmentation model to identify sources, revealing that suburban sewage, soils, and dry/wet deposition are major sources. Suburban sewage had an extremely high MP abundance (520,000 items·m⁻³), indicating it as a significant source. Non-fibrous polypropylene (PP) was mainly controlled by soils, while fibrous polyethylene terephthalate (PET) was influenced by sewage sludge. The study highlights the importance of local field investigations for accurate source apportionment. MPs are ubiquitous in urban environments, with global plastic production reaching 400.3 million tonnes in 2022. MPs are found in various environmental compartments, including marine, freshwater, soil, and atmosphere. Previous studies have primarily used subjective methods to identify MP sources, but data-driven approaches offer more accurate results. The study uses the conditional fragmentation model to analyze MP sources, showing that MPs in rivers and lakes are influenced by multiple sources, while suburban sewage is a major contributor. The study found that MPs in rivers and lakes had high abundance and diversity, with non-fibrous MPs (fragments and films) dominating. Suburban sewage had a high MP abundance, with non-fibrous MPs also prevalent. The study also found that rainfall significantly increased MP abundance in rivers, suggesting it as a major source of diffuse pollution. The pollution risk of MPs in Beijing's water bodies was assessed, with suburban sewage showing the highest risk. The study used the Simpson and Shannon indices to assess MP diversity, finding that rivers and lakes had high diversity, while suburban sewage had high abundance but lower diversity. The conditional fragmentation model was used to determine MP fragmentation and stability, showing that non-fibrous MPs were more stable than fibrous ones. The study also identified soil as a major source of MPs in urban water systems, with PET and fibers being influenced by wastewater and sewage sludge. The study highlights the importance of understanding MP sources in urban environments to develop effective management strategies. It emphasizes the need for systematic approaches to characterize MP contributions from various sources, such as atmospheric deposition, soil, and wastewater. The study provides insights into the fate and sources of MPs in urban water bodies, contributing to a better understanding of their environmental impact.This study investigates the sources of microplastics (MPs) in Beijing's urban water bodies, including rivers, lakes, and suburban sewage. MPs are challenging to trace due to their complex transportability. The research combines MP diversity with a conditional fragmentation model to identify sources, revealing that suburban sewage, soils, and dry/wet deposition are major sources. Suburban sewage had an extremely high MP abundance (520,000 items·m⁻³), indicating it as a significant source. Non-fibrous polypropylene (PP) was mainly controlled by soils, while fibrous polyethylene terephthalate (PET) was influenced by sewage sludge. The study highlights the importance of local field investigations for accurate source apportionment. MPs are ubiquitous in urban environments, with global plastic production reaching 400.3 million tonnes in 2022. MPs are found in various environmental compartments, including marine, freshwater, soil, and atmosphere. Previous studies have primarily used subjective methods to identify MP sources, but data-driven approaches offer more accurate results. The study uses the conditional fragmentation model to analyze MP sources, showing that MPs in rivers and lakes are influenced by multiple sources, while suburban sewage is a major contributor. The study found that MPs in rivers and lakes had high abundance and diversity, with non-fibrous MPs (fragments and films) dominating. Suburban sewage had a high MP abundance, with non-fibrous MPs also prevalent. The study also found that rainfall significantly increased MP abundance in rivers, suggesting it as a major source of diffuse pollution. The pollution risk of MPs in Beijing's water bodies was assessed, with suburban sewage showing the highest risk. The study used the Simpson and Shannon indices to assess MP diversity, finding that rivers and lakes had high diversity, while suburban sewage had high abundance but lower diversity. The conditional fragmentation model was used to determine MP fragmentation and stability, showing that non-fibrous MPs were more stable than fibrous ones. The study also identified soil as a major source of MPs in urban water systems, with PET and fibers being influenced by wastewater and sewage sludge. The study highlights the importance of understanding MP sources in urban environments to develop effective management strategies. It emphasizes the need for systematic approaches to characterize MP contributions from various sources, such as atmospheric deposition, soil, and wastewater. The study provides insights into the fate and sources of MPs in urban water bodies, contributing to a better understanding of their environmental impact.