Cumulative Effects (CE) on ecosystems resulting from anthropogenic activities have been observed qualitatively for centuries and discussed conceptually for decades, but only recently have quantitative approaches that integrate spatial and temporal scales been proposed. Quantitative characterization, however, is limited and the lack of metrics and diagnostic tools to manage CE leaves environmental assessment with unknown viability in Cumulative Effects consideration. In distinguishing between Cumulative Stress (CS) and CE, this study explores the quantitative relationship between recent projections of CS in Lake Huron and fish growth-based model measurements of CE. The results show that not only did the fish-growth based estimates of CE align poorly with CS estimates, but they appear to be confounded by uncertainties in the spatial structure of fish populations within Lake Huron. This may be due to a poor estimate of CS, the growth-based metric of CE or underlying complexity in the system that is confounding mechanistic resolution of CS and CE at this coarse ecosystem scale. Management actions taken to address CE in the face of a weak understanding of aquatic system responses to multiple, interacting stressors may be error prone and ineffective, with the potential to further degrade systems being restored. Identifying a suitable metric for CE remains a priority and should emphasize the following important criteria: 1) Integrate over space; 2) Integrate over time; 3) be responsive to cumulative stress; 4) be neither prohibitively expensive nor complex.