Restoration of river network connectivity has become a major focus of conservation efforts as dams age and as the ecological benefits of free-flowing rivers are recognized. Restored connectivity restores access for migratory fishes that utilize the entire river system for their life cycle, allowing the delivery of material and process subsidies as fish travel to spawn. My work addresses how restored fish subsidies would impact upstream ecosystem processes, and we found that algal growth on control and nutrient-amended substrates correlated with light-dependent nutrient concentrations. Limitations on primary production varied even within one river basin, such that any effect of added nutrients from migratory fish would greatly depend on where the fish travel. Outcomes of nutrient limitation experiments are often assumed to reflect the limitation regime of the larger river system, but this work highlights the importance of local-scale variation in constraints on ecosystem processes when considering impacts of nutrient enrichment.