This opinion paper highlights the concept of transboundary transitional waters (TTW)—A socio-ecosystem category at the interface of freshwater and marine environments that straddle international borders. The central message of the paper is that while the European Union’s Water Framework Directive (WFD) has advanced the recognition and protection of transitional waters, it is insufficient to capture the socio-ecological and political complexities of TTW, especially in regions where countries outside the EU are involved. The sustainable governance of TTW requires recognition of their unique ecological, socio-economic, cultural, and geopolitical dimensions. The paper delivers three main insights. First, it introduces the Emerald Economy as a new concept that integrates Blue and Green Economy principles, establishing an ecosystem-based, transboundary framework to address the ecological, economic, and governance challenges of TTW. Second, the study highlights the methodological principles of combining remote sensing, geostatistical analysis, and spatiotemporal modelling to overcome data fragmentation, identify development patterns, vulnerabilities, and risks in 123 TTW worldwide and reinforce their transboundary monitoring and decision-making. Third, the paper also highlights the critical transboundary governance barriers of political tensions, illicit cross-border activities, and uneven data quality as pivotal yet often overlooked factors that obscure the real picture of cross-border connections, thereby distorting management outcomes. The paper’s concluding statement is that TTW are not only vital ecological corridors but also contested geopolitical spaces, and that their sustainability and resilience, reducing the risks of ecological degradation and geopolitical confrontation, depend on harmonized environmental policies, coordinated mosaic governance, shared scientific research and monitoring platforms, and management strategies that transcend political boundaries.
Dučinskas et al. (Sun,) studied this question.