Rivers unchained: A spatial optimization approach for prioritizing river barrier removal

River fragmentation is a major constraint on ecological status and biodiversity in freshwater systems, creating a need for robust and operational tools to prioritize restoration. We develop a spatially explicit framework for prioritizing river barrier removal that integrates ecological indicators, river network connectivity, and economic constraints within a unified optimization approach. The framework combines a composite ecological benefit index with a dynamic, state-dependent representation of river network connectivity, allowing ecological gains from barrier removal to evolve as downstream and upstream conditions change. By linking connectivity, water quality, and species-specific habitat accessibility, the approach captures how restoration benefits depend on both local conditions and network structure. Applied at a national scale, the model reveals that ecological gains are highly non-linear and strongly shaped by network topology. Optimal restoration strategies form spatially coherent restoration corridors, where removing key bottlenecks unlocks extensive upstream habitats and guides subsequent removals within the same catchments. Restoration priorities vary with budget levels, hydropower opportunity costs, and policy objectives. Incorporating hydropower opportunity costs substantially alters restoration priorities, whereas alternative barrier-hydropower linkage formulations yield broadly similar aggregate outcomes once major hydropower assets are excluded from restoration portfolios. Sensitivity analyses demonstrate that restoration outcomes are influenced by alternative ecological-response formulations and parameterizations but remain primarily driven by river-network structure and dynamic connectivity processes. The results highlight the importance of integrating ecological indicators with dynamic network processes in restoration planning and provide a generalizable framework for supporting large-scale river restoration under competing environmental and economic objectives.