Fragmented Rivers: A Global and Local Challenge

Worldwide, only 37% of rivers longer than 1,000 km still flow freely[1]. The presence of infrastructures such as dams, weirs, and levees disrupts what is known as river ecological continuity, raising both ecological issues (hydrological processes, sediment and organism transport, etc.) and socio-economic concerns (river uses, associated resources, landscape value, etc.).This continuity is a key component of achieving the “good ecological status” of rivers as defined by the European Water Framework Directive (2000/60/EC)[2]. The European Union has committed to restoring 25,000 km of free-flowing rivers by 2030[3].

In mainland France, data from the National Database of Flow Obstacles (ROE) indicate that, on average, there is one obstacle every 4.16 km of river. Numerous restoration projects have been launched over recent years — since 2019, 386 structures have been made passable in the Rhône-Méditerranée basin and 345 in the Loire-Bretagne basin.At the same time, local controversies have arisen. Certain stakeholders[4] have questioned both the methods used to implement these restoration projects and their ecological and social relevance.

In this context, with support from the French Biodiversity Office (OFB), a group of scientists coordinated by INRAE (in collaboration with ENS de Lyon, Aix-Marseille Université, Institut Agro, GRAIE, Université Rennes 2, Université Paris Nanterre, AgroParisTech, CNRS, and Université Lumière Lyon 2) and the French Long-Term Socio-Ecological Research Network (Réseau des Zones Ateliers)[5], has produced a comprehensive synthesis of the current scientific knowledge on river continuity restoration. This collective and interdisciplinary effort—bringing together expertise in aquatic and terrestrial ecology, fluvial geomorphology, sociology, and geography—aims to enrich public debate and provide practical guidance for more effective, socially accepted restoration projects.

Defining Ecological Continuity and Its Multiple Dimensions

The concept of ecological continuity encompasses all the biophysical components of river systems (channels, groundwater, floodplains) and the flows of water, organisms, and materials between them. It also includes a temporal dimension, linked to hydrological processes such as floods and tides, or to the biological rhythms of species.

The experts distinguish three spatial dimensions of continuity:

• Longitudinal continuity (the most familiar): upstream–downstream connections within the main river and its tributaries.
• Lateral continuity: exchanges between the main channel and its floodplain, including periodic overflows.
• Vertical continuity: interactions between the river and the underlying aquifer.

Discontinuity, therefore, refers to interruptions in one or more of these dimensions — not just the longitudinal one. Based on this framework, the researchers compiled and analyzed a broad bibliographic corpus of scientific and technical literature, complemented by field experience and collaborative workshops.

They identified multiple interconnected issues associated with disrupted river continuity — from ecological challenges (maintaining hydrological processes, sediment and organism transport, and ecological functions) to socio-economic concerns (river use, resource management, risk prevention, and landscape value).

Ten Key Points for Effective Restoration Projects

Drawing on lessons learned from past restoration initiatives, the experts propose a strategic approach structured around ten points of attention, to guide decision-making, co-construction, and implementation of river continuity restoration projects.

Their recommendations emphasize that the decision whether or not to restore, and how to do so, must integrate both social and economic dimensions, while respecting the specific geographic and cultural context of each territory.Successful implementation also requires active involvement of all stakeholders throughout the process — a condition for sustainable, shared, and effective restoration aligned with both ecological and societal goals.

[1] Grill G., Lehner B., Thieme M. et al. (2024). Mapping the world’s free-flowing rivers, Nature.
[2] Directive 2000/60/EC of the European Parliament and of the Council of 23 October 2000 establishing a framework for Community action in the field of water policy.
[3] https://environment.ec.europa.eu/news/free-flowing-rivers-commission-advises-how-select-sites-and-finance-removal-obsolete-barriers-2021-12-21_en
[4] A diverse group of stakeholders, including local residents, owners of former mills, and small hydropower operators.
[5] An inter-organizational research network on socio-ecosystems, supported by the CNRS. The *Zones Ateliers* are long-term research observatories established within local territories, focusing on key structuring elements (river systems, agricultural or urban landscapes, natural parks, coastal areas, etc.) to conduct multidisciplinary research and inform public management and policy.