Invasive alien species (IAS) are typically viewed as threats to biodiversity, but they may also serve a valuable role in environmental monitoring. Due to their high abundance, wide distribution, and resilience to environmental stressors, IAS offer practical advantages as bioindicators of pollution, particularly in ecosystems where native species are rare, protected, or declining. Their capacity to bioaccumulate a broad range of contaminants, including trace elements, persistent organic pollutants, and emerging contaminants such as PFAS and microplastics, makes them effective tools for assessing environmental quality. For example, bivalves like Dreissena polymorpha are efficient accumulators of mercury; crustaceans such as Procambarus clarkii have been shown to reflect microplastic pollution; and semiaquatic mammals like Myocastor coypus can help detect wetland contamination through fecal analysis. Importantly, using IAS can reduce ethical and legal concerns tied to sampling vulnerable native species. However, challenges remain. Physiological and ecological differences between IAS and native species can influence contaminant uptake and lead to inconsistent or misleading results. There are also regulatory and ecological risks, including the potential to unintentionally support the spread of invasive species through monitoring programs. To overcome these limitations, IAS should be used strategically, focusing on established populations and interpreting their data alongside that of native species. When applied carefully, IAS can complement traditional monitoring tools, offering a cost-effective, ethically sound, and ecologically informative approach to tracking environmental pollution and supporting conservation efforts.