A Hybrid Nature-Based and Adaptive Ecohydraulic Barrier for Selective Sea Lamprey Control

River barriers used for invasive species management can create a conflict between biological control and the restoration of longitudinal ecological connectivity. In particular, structures designed to restrict the upstream migration of invasive sea lamprey may also impede native fish movement, alter local habitat conditions, and reduce continuity within river ecosystems. This study presents a conceptual hybrid nature-based solution that combines ecological restoration principles with an adaptive ecohydraulic barrier intended to support selective sea lamprey management while maintaining greater river connectivity. The proposed concept consists of a floating, vertically adjustable rotating cylinder combined with a permeable lower screen and integrated within a broader river-restoration setting. Rather than assessing hydraulic performance quantitatively, the study evaluates the concept from a nature-based perspective by considering adaptability to natural water-level variability, ecological connectivity, reversibility, habitat integration, passive operation, biodiversity co-benefits, maintenance requirements, and potential environmental trade-offs. The conceptual design is also considered in relation to conventional fixed barriers and nature-oriented river-restoration approaches. The proposed framework indicates that combining adaptive engineering with nature-based river-management measures could provide a more flexible alternative to permanently fixed barriers. Vertical adjustability may accommodate changing river stages, while the permeable lower section may improve hydraulic and ecological continuity. Integration with riparian restoration, heterogeneous channel habitats, refuge areas, and nature-like passage features could further enhance ecological functionality. Nevertheless, important uncertainties remain regarding species selectivity, debris accumulation, maintenance, mechanical reliability, and unintended passage of invasive organisms. The proposed system is best interpreted as a hybrid nature-based–engineered intervention rather than a purely nature-based structure. Its principal contribution is a conceptual pathway for reconciling invasive species control with river connectivity and ecological restoration.