Restoring natural functions of rivers

Why river functions matter

Healthy rivers are dynamic ecosystems whose ecological health depends on the continuous interaction between water, sediment, vegetation and surrounding landscapes. These interactions occur along the river (longitudinal connectivity), between the river and its floodplain (lateral connectivity), with groundwater (vertical connectivity), and over time as rivers naturally adjust to changing conditions.^[1],[2],[3]

The natural flow regime—including seasonal floods, low flows and variations in discharge—drives many of the physical and ecological processes that shape river ecosystems.^[4] Water transports sediment, creating a diverse mosaic of habitats such as riffles, pools, gravel bars and side channels that support fish, macroinvertebrates and aquatic plants.^[5],[6] At the same time, the exchange of water, sediment, nutrients and organisms between rivers, floodplains and groundwater sustains ecological productivity, biodiversity and water quality.^[7],[8],[3]

When these natural processes function together, rivers continually create and renew habitats, transport nutrients and organic matter, and maintain resilient ecosystems that can adapt to environmental change.^[9],[2] Healthy rivers also provide essential ecosystem services, including flood attenuation, groundwater recharge, sediment regulation, carbon storage, clean drinking water and habitat for threatened species, delivering substantial environmental, social and economic benefits.^{[10],[11],[12]}

How rivers have been altered

Over the past centuries, European rivers have been extensively modified to support navigation, hydropower, flood protection, agriculture and urban development.^{[13],[14],[15]} Today, Europe’s rivers are among the most fragmented in the world, interrupted by more than one million artificial barriers—including dams, weirs, sluices, culverts and ramps—of which an estimated 150,000 to 200,000 are obsolete.^{[16],[17],[3]}

These barriers interrupt river connectivity, preventing fish migration and disrupting the natural transport of sediment, nutrients and organic matter. Sediment becomes trapped upstream, while downstream river reaches experience erosion, riverbed incision and habitat degradation.^{[18],[19],[20]}

At the same time, water abstraction, dams and flow regulation have altered natural flow regimes, reducing seasonal flood pulses and changing water temperatures and flow patterns.^{[18],[21],[22]} Channel straightening, bank reinforcement, levee construction and the removal of woody debris have simplified river morphology and disconnected rivers from their floodplains, reducing habitat diversity and limiting natural river dynamics.^{[23],[15],[24]}

The cumulative effects of these alterations have led to severe ecological degradation. Populations of migratory freshwater fish have declined by 93% since 1970, wetland and riparian habitats have been lost or degraded, and many European rivers still fail to achieve the good ecological status required under EU legislation.^{[25],[26],[27]}

What Restoring River Functions Means

River restoration is increasingly shifting from repairing individual habitats towards restoring the natural processes that allow rivers to function as dynamic ecosystems.^{[28],[2],[29]} Rather than creating static habitats, process-based restoration aims to recover the hydrological, geomorphological and ecological processes that sustain healthy rivers over the long term.

A key objective is to restore more natural flow regimes by implementing environmental flows that maintain seasonal low flows, channel-forming floods and natural flow variability. These processes sustain habitat diversity, transport sediment and provide essential ecological cues for aquatic species such as spawning fish.^{[4],[30],[22]}

Restoring sediment continuity is equally important. Measures such as reducing sediment trapping by reservoirs, reintroducing gravel downstream of dams, sediment bypass systems and controlled flushing flows help re-establish natural sediment transport, rebuild riverbeds and improve spawning habitats.^{[31],[32],[20]} Improving river connectivity is another central objective. Removing obsolete dams and weirs, adapting unavoidable barriers, restoring side channels and reconnecting rivers with their floodplains allow fish, sediment, nutrients and water to move freely through the river system.^{[33],[34],[16]} Where appropriate, removing or relocating levees gives rivers more space to function naturally while increasing floodwater storage and restoring floodplain processes. Finally, restoring riparian vegetation and natural channel complexity strengthens ecosystem resilience. Re-meandering straightened rivers, restoring native riparian forests, adding large woody material and allowing rivers to reshape their channels create diverse habitats, improve water quality, regulate stream temperatures and support a rich diversity of aquatic and terrestrial species.^{[35],[36],[37],[38],[2]}

By restoring these natural processes, river restoration contributes not only to healthier ecosystems but also to climate adaptation, flood risk reduction, improved water quality and more resilient landscapes. These multiple benefits underpin the objectives of European water, biodiversity and climate policy and make process-based restoration an essential component of sustainable river basin management.

Contribution to EU restoration objectives

The Nature Restoration Regulation (EU) 2024/1991 strengthens the existing EU policy framework for river restoration by introducing legally binding targets for restoring river connectivity and ecological functioning. The Water Framework Directive (2000/60/EC) already established the objective of achieving good ecological status for all surface waters, including improvements in hydromorphological conditions and river continuity. However, the WFD does not generally require the removal of barriers or the restoration of natural river dynamics unless these measures are necessary to achieve good ecological status.

The Nature Restoration Regulation builds upon this framework by introducing a stronger focus on restoring free-flowing rivers. It requires Member States to restore at least 25,000 km of free-flowing rivers by 2030, primarily through the removal of obsolete barriers and complementary measures that improve river connectivity. Restoring free-flowing rivers means re-establishing the natural movement of water, sediment and organisms throughout the river system. This includes improving longitudinal connectivity for fish migration, restoring sediment transport processes and reducing the fragmentation caused by dams, weirs and other artificial structures.

River connectivity is also closely linked to the connection between rivers and their surrounding landscapes. Where appropriate, restoration can include reconnecting rivers with their floodplains, removing or relocating levees, and restoring more natural flow patterns. These measures allow rivers to respond dynamically to changing conditions, improve habitat availability and increase resilience to climate change impacts such as floods and droughts. River restoration contributes directly to wider European climate and environmental objectives. The EU Climate Law (EU 2021/1119) establishes climate neutrality by 2050 and recognises the role of healthy ecosystems in climate mitigation and adaptation. The EU Adaptation Strategy (2021) promotes nature-based solutions that increase resilience to climate impacts. By restoring natural river processes, improving connectivity and allowing rivers more space to function, restoration measures can simultaneously support biodiversity, climate adaptation and sustainable water management.

For policymakers and practitioners, this means that measures such as barrier removal, fish passage improvements, restoring sediment continuity, reconnecting floodplains and relocating levees can contribute to multiple EU objectives simultaneously. They support the achievement of ecological objectives under the Water Framework Directive, contribute to the conservation objectives of the Habitats Directive (92/43/EEC) and Birds Directive (2009/147/EC), and directly support the legally binding restoration targets of the Nature Restoration Regulation.

Key river functions to restore

Successful river restoration focuses on restoring natural processes rather than creating individual habitats. The functions below form the basis of process-based river restoration and are closely linked. Depending on the pressures affecting a river, projects may focus on one or several of these functions.

The five functions

Useful European resources

The following platforms provide practical guidance, case studies and technical tools for river restoration projects: