21 May 2025 – A new scientific study, led by researchers from the University of Natural Resources and Life Sciences (BOKU) in Vienna and the Hellenic Centre for Marine Research (HCMR) in Athens, highlights severe ecological consequences due to the lack of ecological flow from the Aoos Springs dam. This absence is disrupting both the river’s biodiversity and its natural hydrological regime.
According to the EU Water Framework Directive, ecological flow is not simply a minimum water volume, but the amount of water necessary for downstream ecosystems to maintain their natural characteristics and carry out vital ecological functions. Under the provisions of both the EU Water Framework Directive (2000/60/EC) and the Habitats Directive (92/43/EEC), member states are required to ensure adequate hydrological flow to achieve "good ecological status" and to protect designated species and habitats—many of which depend directly on continuous river flow. Despite this, Greek legislation does not currently require the establishment of ecological flow for large hydroelectric dams.

The Aoos/Vjosa, one of Europe’s last free-flowing rivers, stretches for 260 km from its source in Greece, flowing through the Northern Pindos National Park and 13 Natura 2000 sites before crossing into Albania, where it forms the Vjosa Wild River National Park and eventually empties into the Adriatic Sea. It forms a vital ecological corridor and a transboundary ecosystem recognized under both European and national legislation. However, the construction of the Aoos Springs dam in 1987, part of a key hydroelectric infrastructure project and artificial reservoir, completely cut off water flow to the river’s downstream section, triggering a cascade of severe ecological impacts.

The study—published by Riverwatch, EuroNatur, and MedINA, as part of the international alliance Save the Blue Heart of Europe—highlights the urgent need to restore ecological flow at the Aoos Springs dam. Key findings include:
•    With no ecological flow from the Aoos Springs dam, the once free-flowing river has been reduced to a narrow stream just 1.3 meters wide. This has triggered drastic hydromorphological changes and severely degraded the surrounding riparian ecosystem.
•    The absence of ecological flow has caused drastic habitat loss and a significant decline in fish diversity and populations—particularly affecting species like the Balkan trout (Salmo farioides), which is protected under the EU Habitats Directive.
•    These impacts are most critical during the dry summer months and extend into the Northern Pindos National Park and three Natura 2000 sites, raising urgent concerns under current climate crisis conditions.

The study underscores the urgent need to restore ecological flow to safeguard the river’s biodiversity. It recommends implementing both a year-round minimum flow and dynamic seasonal variations to support fish reproduction, sediment transport, and natural riverbed renewal.

“The Aoos is not just a river. It is a vital artery of life, connecting ecosystems, communities, and cultural heritage. Ensuring ecological flow must become a cornerstone of public policy for the region’s sustainable future.”, Alexis Katsaros, Executive Director of Medina