Assessing River Ecological Status Under the Water Framework Directive ^†

Abstract

Introduction: Despite more than two decades of implementation, the European Water Framework Directive (WFD) still faces major challenges in achieving good ecological status across European water bodies. Key limitations persist in connectivity restoration, transboundary harmonization, monitoring network design, and biological assessment of complex systems such as large rivers, reducing the Directive’s capacity to provide consistent ecological diagnoses and support effective river basin management. Objective: This work had four objectives: (I) incorporate ecological status into connectivity assessments; (II) evaluate harmonization in Iberian transboundary basins; (III) optimize the national fish monitoring network through co-creation; (IV) develop a fish-based multimetric index for Portuguese large rivers. Methodology: The work combined four approaches: (1) graph-based connectivity analysis integrating the probability of achieving good ecological status to evaluate functional connectivity across European river networks; (2) cross-border comparison of ecological classifications between Portugal and Spain in shared Iberian basins; (3) optimization of the Portuguese fish monitoring network through a co-creation approach involving the national authority; (4) development of a fish-based multimetric index designed for Portuguese large rivers. Results: Integrating ecological status into connectivity analyses reduced estimated connectivity and highlighted the combined effects of fragmentation and degradation. Cross-border comparisons showed that formal harmonization does not ensure consistent ecological classification. The optimized monitoring networks improved ecological representativeness without increasing sampling effort, while co-creation ensured operational feasibility. The new fish index for large rivers captures spatial variation in ecological quality and responds to pressure gradients, addressing a recognized methodological gap. Conclusions: Improving WFD implementation requires progress across multiple complementary components rather than isolated advances. More effective river management depends on integrating ecological processes, comparable assessment outputs, representative monitoring networks, and system-specific tools. These approaches provide transferable pathways for strengthening freshwater assessment and supporting more coherent river restoration and management across Europe.