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Invasive species are a known stressor on aquatic ecosystems, particularly in the waters of the Great Lakes basin. A recent invader, Hemimysis anomala, has had significant impacts on food webs in Europe, where it invaded previous to its spread to North America. This study used carbon and nitrogen stable isotopes to characterize and compare the diet of Hemimysis from 13 sites in the Great Lakes basin. Results indicated that: (i) Hemimysis relied predominantly on pelagic carbon sources at the majority of sites, and isotopic differences between life-stages existed at two of the 13 sites examined, (ii) the trophic offset and reliance on pelagic food sources did not differ significantly between lotic and lentic sites, and (iii) the isotopic niche width of Hemimysis was spatially heterogeneous, varying by an order of magnitude among sites, but was unrelated to the degree of isotopic variation in the basal food web at each site. Observed ranges in trophic offset and the pelagic fraction of dietary carbon indicate that Hemimysis derives carbon from both benthic and water column sources, as well as at multiple trophic levels. Our results support the view that Hemimysis is an opportunistic omnivore that displays significant dietary flexibility.