Physical heterogeneity is a strong driver of ecosystem function in rivers, but it is not clear whether this relationship persists in "Anthropocene" rivers: those affected by pronounced and persistent anthropogenic stressors. Such stressors can result in regime shifts of rivers, altering not only ecosystem structure and function, but also their heterogeneity. This study examines the heterogeneity of the physical template and ecosystem function of the Illinois River (Illinois, USA), as an example of an Anthropocene River. This river was biologically dead for most of its length in the mid 1900′s because of multiple anthropogenic stressors. A systemic reduction in physical heterogeneity of the Illinois River also resulted in simplification of its physical environment. Multiple lines of evidence demonstrate the physical simplification of the river channel caused the homogenization of ecosystem function. The significant overlap in trophic niche spaces, convergence of isotope ratios, dominance of benthic contributions to higher-level consumers, increased food chain lengths, plus the emergence of only two food webs indicate a simpler river ecosystem. Limited attention to the role of heterogeneity in anthropogenically modified river systems not only restricts understanding of resilience in rivers, but also the application of resilience thinking to managing these globally important ecosystems.