Elodea canadensis is a widespread invasive alien aquatic species in Europe. However, there is growing evidence that increasing anthropogenic eutrophication and other factors are leading to a decline in the populations of this species. We compared the structure of plant communities and the phenotypic plasticity of E. canadensis individuals across communities in Ukraine and Portugal to assess whether the species responds similarly to environmental variation, and to identify differences in its distribution, community role, and the environmental factors influencing the formation of morphological traits of the species and biomass. In both countries, E. canadensis preferentially occurs in oligo-mesotrophic and meso-eutrophic waters, forming similar communities, but in Ukraine the communities in lentic water bodies were floristically more diverse. Populations with high biomass of E. canadensis in Ukraine were formed in lentic water bodies with good water exchange, as well as in lotic ecosystems of both Ukraine and Portugal. Environmental clustering revealed a distinct ecological separation among water bodies, with the strongest contrast observed between lower-nutrient, higher-elevation Ukrainian lakes and nutrient-rich, lowland mixed lotic systems in both countries. The morphological traits of E. canadensis differed significantly between these clusters, particularly shoot length and leaf width, highlighting phenotypic responses to environmental gradients. We assume that anthropogenic eutrophication affects E. &amp; scy;anadensis communities, and may lead to their decline or disappearance as trophic levels rise in both countries. Understanding these patterns is important for forecasting invasion dynamics under eutrophication and climate change, and for refining management strategies in freshwater ecosystems.< Leer menos