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Why to remove a dam

Barrier removal has become one of the most effective and rapidly growing nature-based solutions for restoring river connectivity and recovering freshwater ecosystems (Darre et al. ,2025). For centuries, European rivers have been modified by human-made structures such as dams, weirs, culverts, and other barriers built for different purposes. Today, many of these structures have lost their original function and are considered obsolete. It is estimated that there are around 156.000 obsolete barriers across Europe (Belleti et al., 2020). In recent years, barrier removal has gained strong momentum as a practical restoration measure, bringing a wide range of benefits. From ecological recovery to socio-economic improvements, removing obsolete barriers helps rivers regain their natural dynamics and supports both nature and people.

Below, we explain why:  

Removal of Ackers Weir in the United Kingdom

The removal of the Ackers Weir on the River Cole in the United Kingdom in 2022 contributed to improvements in water quality and flow. The weir resulted in the accumulation of contaminated sediments being trapped upstream. Contaminated sediments were treated simultaneously with the removal of the weir. As a result, contaminated sediments could not be washed downstream. Barrier removal also contributed to natural river flow and restoring downstream sediment movement (GOV UK Environment Agency, 2023; Sanctus, n.d.).

Improves water quality and natural flow

Restoring connectivity through barrier removal leads to improved water quality and reestablished natural flow, reversing the detrimental effects of impounded or slow-moving water, like oxygen depletion, faster organic decomposition and nutrient imbalances, and conditions that favor toxic algae blooms (Bednarek, 2001; Winton et al., 2019; Maavara et al., 2020; Abbott et al., 2022). 

Image 1. Ackers Weir (GOV UK Environment Agency, 2023)

Decreases the risk of flooding

Barrier removals contribute to flood protection. The removal of transversal structures alleviates the risk of flooding by decreasing water-surface elevation during high flow events and by preventing incisions (i.e., deepening of river channels due to erosion) that disconnect the river from its floodplain (Olson and Simeone, 2021; Knox et al., 2022). The removal of lateral barriers (levees, embankments & floodwalls), which interrupt the hydrological connectivity between rivers and their floodplains, re-establishes overbank flow, resulting in improved flood storage, with increased water retention volumes and duration (Clilverd et al., 2013).

Removal of San Marcos Weir in Spain

The San Marcos weir on the Bernesga River in León, Spain, provided safety benefits in the area. The weir was partially demolished in 2013 to reduce flood risks. A year after the removal, a significant flood event occurred. This flood would have flooded part of the city of León if the weir had not been partially removed (Confederación Hidrográfica del Duero, 2013; Restoring Europe’s Rivers, 2019). 

Figure x: Water levels before and after the San Marcos Weir removal taken by José Ignacio Santillán Ibañez (Duero River Basin Authority)

Image 2: Water levels before and after the San Marcos Weir removal taken by José Ignacio Santillán Ibañez (Duero River Basin Authority)

Results in cooler water temperatures and mitigates against climate change

Barrier removals increase ecological resilience in the face of changing climates in several different ways (Hart et al., 2002; Parasiewicz et al., 2022; Fovet et al., 2023). Removing barriers allow for a faster recovery of freshwater ecosystems from climate-induced disturbances (Zaidel et al., 2021), it increases access of freshwater species to thermal and flow refugia (Abbott et al 2024),  and it reduces the overall temperature of free-flowing water, benefiting fish and other species (Lessard & Hayes, 2003).

The Removal of Dams in Sélune River in France

The removal of the dams on the Sélune River in France in 2022 had a positive effect on water temperature, among other benefits. Scientists found that, after dam removal, the river’s temperature downstream decreased by 2°C during the hottest period of summer, compared with previous years (Dam Removal Europe, 2019; MacErlean, 2025; Fovet et al., 2023).

Image 3: Vezins Dam taken by Iwan Hoving – WFMF (Dam Removal Europe, 2019)

Alleviates safety risks

Approximately 156,000 barriers in Europe are obsolete (Beletti et al., 2020). Some of them pose a breach risk that threatens human safety and property. Barrier removal can alleviate such incidents, save lives and prevent spending millions in repairing damages (Bellier, 1967, in Biscarini et al., 2016). In addition, low-head barriers (i.e., weirs), among other types of barriers, are dangerous due to the formation of an inescapably strong subsurface current (submerged hydraulic jump). These structures, usually called “drowning machines”, have caused hundreds of fatalities in Europe and the USA (Mouchlianitis, 2024; Clark and Wheeler, 2023). Removal of such barriers – especially if obsolete – can save human lives.  

The Removal in Pčinja River basin in North Macedonia

North Macedonia’s first barrier removal in the Pčinja River basin in 2025 has helped alleviate safety risks. Eko-svest removed 2 barriers, restoring 72 km of river. As a result of the successful project, flood and safety risks for communities were reduced (Open Rivers Programme, n.d.-a).

Image 4. Removal on Pčinja River, North Macedonia – Eko-svest (Open Rivers Programme ,n.d. -a)

Generates income opportunities & supports local communities with amenity value

Nature restoration measures, like barrier removal, return the initial investment 8- to 38-fold through the gained ecosystem services (European Commission, 2022). In addition, barrier removal can be presented as a business model for construction companies (Macdonald, 2025). Finally, barrier removal supports recreational businesses or activities such as angling, canoeing, kayaking, swimming, wildlife viewing and hiking (Born et al., 1998; Leisher et al., 2021).

The Removal in Havørred Fyn project in Denmark

The removal of barriers began in the 1990s with the Havørred Fyn project in Denmark, which supported local communities through angling tourism. Barrier removal in Havørred Fyn generated an estimated 5.8 million euros per year in angling tourism, compared to a 0.5 million euro per year initial investment through dam removal (The Nature Conservancy, n.d.; Havørred Fyn, n.d.). 

Image 5. Seatrout Fyn (Havørred Fyn, n.d.)

Eliminates maintenance/ operational/ upgrading costs

Many barriers are no longer profitable, yet require maintenance and have operational costs. Removing such infrastructure eliminates any unnecessary costs. Barriers also age and need to be repaired/upgraded to meet the latest engineering and environmental standards. Barrier removal is often way less expensive than the repair works, and thus a much more appealing option to barrier owners (Born et al., 1998; Kitchen et al., 2016). 

The Removal of hydropowers in River Hiitolanjoki in Finland

The removal of 3 hydropower plants on the River Hiitolanjoki, Finland, was completed in 2023. The barrier removal not only benefited the ecological restoration of the rivers but also benefited the dam owners economically. The dams were sold based on evaluations of electricity production, which concluded that they had become unprofitable, given maintenance and mandatory environmental measures (Dam Removal Europe, n.d.-a, Lozza, 2024).

Image 6. Demolishing of a Dam in Hiitolanjoki River (taken by Mikko Nikkinen in Dam Removal Europe, n.d.-a)

Restores threatened floodplain forest and wetlands

Barriers impact the natural flooding regimes of floodplains (EEA, 2019). Sediment trapping by barriers results in downstream sediment shortages, which erode riverbeds and banks rather than depositing material. Over time, the deepening of the channels (incisions) lowers the river’s elevation relative to the floodplain.  This confines water within the riverbanks and disconnects the river from the floodplain, adversely affecting biodiversity that depends on these floodplains, including aquatic vegetation, waterbirds, and invertebrate populations (Wenskus et. al, 2025; Fields et. al,   2025; Merlin, 2024).

The Removal in Foki sidearm in Slovakia

Barrier removal started in 2023 in Slovakia, aimed at reconnecting the Foki side arm to the main Danube riverbed. Due to construction work and a dam built in 1992, the side arm was disconnected, resulting in the deterioration of habitats and species populations. Removing barriers improved the overall water supply and restored floodplain forests and wetlands in the area. In addition, the restored side arm provided a place for the reproduction and survival of rheophilic fish and rare species of other aquatic organisms (BROZ, 2023; Petrač, 2025). 

Image 7. Foki Arm after Barrier Removal (WWF-Slovakia, n.d.)

Restores sediment transport, avoiding infrastructure collapse, incision and eroding deltas

Many barriers trap sediment impeding its natural deposition around bridge piers and other instream infrastructure, as well as in estuaries and river deltas (Aoula et al., 2021; Pizarro et al. 2020). Removal of barriers restores local natural sediment flow and deposition, which takes a longer (multi-year) period and is driven by events like floods and high flows and thus prevent structural issues, and increase deltas and estuaries’ resilience against sea level rise, storm surges and salt water intrusion (Cheng & Granata, 2007; Fields et al., 2025; Dunn et al., 2009).

The Removal of Hornbachsperre in Austria

The Hornbachsperre on the river Lech in Austria was a sediment-control dam. Due to trapped sediments behind the dam, the lack of sediments on the river resulted in riverbed degradation and habitat disconnection. The aim was to restore the river from 2001 to 2006 and from 2016 to 2021 by releasing sediment through the dam removal. After the removal, the release of sediment contributed to flood protection and increased groundwater levels (WWF, 2021).

Image 8. Hornbachsperre (taken by Toni Vorauer in WWF, 2021)

Increases freshwater biodiversity, including endemic and threatened species

Barriers are a major pressure on freshwater biodiversity (Reid et al., 2018; Tickner et al. 2020). Freshwater migratory fish in particular have suffered a 93% decrease in their populations in Europe since 1970, mainly due to river fragmentation by manmade barriers (Deinet et al., 2024). Barrier removal restores fish passage and thus fish populations, but also favors macro-invertebrate biodiversity, boosts plant biodiversity, and restores connectivity, also benefiting other aquatic species, like otters (Zydlewski et al., 2023; Santucci et al., 2005; Maloney et al. 2008; Shafroth et al., 2002; Brown et al., 2022;  Kloskowski et al. 2013).

The Removal of Culverts in Rulles Basin in Belgium

The removal of 14 culverts in Rulles Basin, Belgium, from 2024 to 2025 connected 33 km of ecologically valuable headwaters. As a result, fish passaging of brown trout, European bullhead, and European brook lamprey was documented. Additionally, as a result of cohabitation with brown trout, the endangered freshwater pearl mussel’s long-term survival was established (Dam Removal Europe, n.d.-b).

Image 9. Removal of Culverts in Rulles Basin (Dam Removal Europe, n.d.-b)

Removing obsolete barriers to comply with legislation

Removing damaged, obsolete and unmaintained barriers contributes to complying with global and EU legislation, including, Global Convention of Biodiversity, Convention on Migratory Species (CMS), RamsarConvention on Wetlands, Convention on Biological Diversity (CBD), Bern Convention, World Heritage Convention and Sustainable Development Goals (SDG 6, 13, 14, 15). In Europe, the EU Water Framework Directive (WFD), the EU Birds & Habitats Directive, the EU floods directive, and the recently adopted Nature Restoration Regulation (NRR), which -among other things- legally requires member states to open up 25,000km of free-flowing rivers by removing obsolete barriers. 

The Removal of Barriers in Vindel River in Sweden

The removal of 5 migration barriers in the Vindel River, Sweden, in 2025 opened up more than 100 km of river in the Nature2000 site and UNESCO biosphere reserve. Aside from the ecological benefits of the removal, the project supported the legally binding European Union (EU) target of restoring at least 25.000 km of rivers within the EU Nature Restoration Law (Open Rivers Programme, n.d.-b).

Image 10. the Vindel River in Sweden (Open Rivers Programme, n.d.-b)