Microplastic pollution is a growing global environmental concern, significantly impacting aquatic ecosystems. In metal mining regions, acid mine drainage (AMD) can exacerbate the issue as microplastics may carry heavy metals, heightening the risks to both human health and ecosystems. AMD can also form a distinct plastisphere further influencing the behavior and distribution of heavy metals. This study, beginning with tailing storage, examined microplastic contamination in river water and sediment in a mining region of South China. The concentration of microplastics in water ranged from 0.2 to 6.2 items/L, predominantly comprising PS, PE and PP. In contrast, the concentration of microplastics in the sediments ranged from 14.1 to 84.8 items/kg and were mainly composed of PP. Most microplastics in both water samples and sediments are smaller than 100 microns. Industrial wastewater from mining activities was identified as the predominant source of microplastics in the AMD-polluted upstream areas while agricultural and domestic waste contributed more significantly in the downstream areas. Plastisphere biodiversity was enhanced, while the colonization of pivotal species on plastic substrates was significantly facilitated in AMD-polluted aquatic environments. In these environments, the ecological niche afforded by plastics was of ecological significance. This study offers the direct evidence of microplastic pollution and highlights the critical ecological role of microplastics in aquatic ecosystems affected by AMD.