Rivers support some of Earth’s richest biodiversity1 and provide essential ecosystem services to society2, but they are often fragmented by barriers to free flow3. In Europe, attempts to quantify river connectivity have been hampered by the absence of a harmonized barrier database. Here we show that there are at least 1.2 million instream barriers in 36 European countries (with a mean density of 0.74 barriers per kilometre), 68 per cent of which are structures less than two metres in height that are often overlooked. Standardized walkover surveys along 2,715 kilometres of stream length for 147 rivers indicate that existing records underestimate barrier numbers by about 61 per cent. The highest barrier densities occur in the heavily modified rivers of central Europe and the lowest barrier densities occur in the most remote, sparsely populated alpine areas. Across Europe, the main predictors of barrier density are agricultural pressure, density of river-road crossings, extent of surface water and elevation. Relatively unfragmented rivers are still found in the Balkans, the Baltic states and parts of Scandinavia and southern Europe, but these require urgent protection from proposed dam developments. Our findings could inform the implementation of the EU Biodiversity Strategy, which aims to reconnect 25,000 kilometres of Europe’s rivers by 2030, but achieving this will require a paradigm shift in river restoration that recognizes the widespread impacts caused by small barriers.
This is a preview of subscription content, access via your institution
Open Access articles citing this article.
Nature Sustainability Open Access 26 January 2023
Seasonal migration and habitat use of adult barbel (Barbus barbus) and nase (Chondrostoma nasus) along a river stretch of the Austrian Danube River
Environmental Biology of Fishes Open Access 08 October 2022
Scientific Reports Open Access 12 April 2022
Subscribe to Nature+
Get immediate online access to Nature and 55 other Nature journal
Subscribe to Journal
Get full journal access for 1 year
only $3.90 per issue
All prices are NET prices.
VAT will be added later in the checkout.
Tax calculation will be finalised during checkout.
Get time limited or full article access on ReadCube.
All prices are NET prices.
Data for the AMBER Barrier Atlas (Fig. 1), observed barrier densities (Fig. 2a), ground-truthed barrier densities (Fig. 2b) and modelled barrier densities (Fig. 2c) are freely available at https://amber.international/european-barrier-atlas/ as well as at https://doi.org/10.6084/m9.figshare.12629051 under a CC-BY-4.0 license. Data for ground-truthed surveyed reaches (Extended Data Table 1, Extended Data Fig. 3) are also available at https://doi.org/10.6084/m9.figshare.12629051 under a CC-BY-4.0 license. Results of walkover surveys in test rivers (Extended Data Table 1), and barrier database sources (Table 1) are also available at https://doi.org/10.6084/m9.figshare.12629051. Source data are provided with this paper.
The Python code used for modelling of barrier abundance, with links to GIS files for visualization, is available under a GNU (https://en.wikipedia.org/wiki/GNU_Project) General Public License at https://github.com/AMBER-data/atlas-model. Protocols used for barrier database management, duplicate exclusion and processing were done manually in SQL and QGIS using ad hoc procedures and are not deposited in a repository.
Reid, A. J. et al. Emerging threats and persistent conservation challenges for freshwater biodiversity. Biol. Rev. Camb. Phil. Soc. 94, 849–873 (2019).
Grizzetti, B. et al. Relationship between ecological condition and ecosystem services in European rivers, lakes and coastal waters. Sci. Total Environ. 671, 452–465 (2019).
Grill, G. et al. Mapping the world’s free-flowing rivers. Nature 569, 215–221 (2019).
Vannote, R. L., Minshall, G. W., Cummins, K. W., Sedell, J. R. & Cushing, C. E. The river continuum concept. Can. J. Fish. Aquat. Sci. 37, 130–137 (1980).
Vitousek, P. M., Mooney, H. A., Lubchenco, J. & Melillo, J. M. Human domination of Earth’s ecosystems. Science 277, 494–499 (1997).
Carpenter, S. R., Stanley, E. H. & Zanden, M. J. V. State of the world’s freshwater ecosystems: physical, chemical, and biological changes. Annu. Rev. Environ. Resour. 36, 75–99 (2011).
Fuller, M. R., Doyle, M. W. & Strayer, D. L. Causes and consequences of habitat fragmentation in river networks: river fragmentation. Ann. NY Acad. Sci. 1355, 31–51 (2015).
Van Looy, K., Tormos, T. & Souchon, Y. Disentangling dam impacts in river networks. Ecol. Indic. 37, 10–20 (2014).
Kemp, P. & O’Hanley, J. Procedures for evaluating and prioritising the removal of fish passage barriers: a synthesis. Fish. Manag. Ecol. 17, 297–322 (2010).
Lehner, B. et al. High-resolution mapping of the world’s reservoirs and dams for sustainable river-flow management. Front. Ecol. Environ. 9, 494–502 (2011).
Lehner, B. et al. Global Reservoir and Dam Database version 1 (GRanDv1) https://doi.org/10.7927/H4N877QK (NASA Socioeconomic Data and Applications Center, 2011).
Mulligan, M., Soesbergen, A. V. & Sáenz, L. GOODD, a global dataset of more than 38,000 georeferenced dams. Sci. Data 7, 31 (2020).
Garcia de Leaniz, C., Berkhuysen, A. & Belletti, B. Beware small dams, they can do damage too. Nature 570, 164 (2019).
Mantel, S. K., Rivers-Moore, N. & Ramulifho, P. Small dams need consideration in riverscape conservation assessments: small dams and riverscape conservation. Aqua. Conserv. Mar. Freshw. Ecosyst. 27, 748–754 (2017).
Lucas, M. C., Bubb, D. H., Jang, M.-H., Ha, K. & Masters, J. E. G. Availability of and access to critical habitats in regulated rivers: effects of low-head barriers on threatened lampreys. Freshw. Biol. 54, 621–634 (2009).
Birnie-Gauvin, K., Aarestrup, K., Riis, T. M. O., Jepsen, N. & Koed, A. Shining a light on the loss of rheophilic fish habitat in lowland rivers as a forgotten consequence of barriers, and its implications for management. Aqua. Conserv. Mar. Freshw. Ecosyst. 27, 1345–1349 (2017).
Magilligan, F. J., Nislow, K. H. & Renshaw, C. E. in Treatise on Geomorphology (ed. Shroder, J. F.) 794–808 (Academic Press, 2013).
Petts, G. E. & Gurnell, A. M. Dams and geomorphology: research progress and future directions. Geomorphology 71, 27–47 (2005).
Bizzi, S. et al. On the control of riverbed incision induced by run-of-river power plant. Wat. Resour. Res. 51, 5023–5040 (2015).
Jones, P. E., Consuegra, S., Börger, L., Jones, J. & Garcia de Leaniz, C. Impacts of artificial barriers on the connectivity and dispersal of vascular macrophytes in rivers: a critical review. Freshw. Biol. 65, 1165–1180 (2020).
Carpenter-Bundhoo, L. et al. Effects of a low-head weir on multi-scaled movement and behavior of three riverine fish species. Sci. Rep. 10, 6817 (2020).
Graf, W. L. Dam nation: a geographic census of American dams and their large-scale hydrologic impacts. Wat. Resour. Res. 35, 1305–1311 (1999).
Jones, J. et al. A comprehensive assessment of stream fragmentation in Great Britain. Sci. Total Environ. 673, 756–762 (2019).
Grizzetti, B. et al. Human pressures and ecological status of European rivers. Sci. Rep. 7, 205 (2017).
Mauch, C. & Zeller, T. (eds) Rivers in History: Perspectives on Waterways in Europe and North America (Univ. of Pittsburgh Press, 2008).
Petts, G. E., Möller, H. & Roux, A. L. Historical Change of Large Alluvial Rivers: Western Europe 355 (John Wiley and Sons, 1989).
Kemp, P. S. in Freshwater Fisheries Ecology (ed. Craig, J. F.) 717–769 (Wiley, 2015).
European Environment Agency in European Waters—Assessment of Status and Pressures 85 (EEA, 2018).
Garcia de Leaniz, C. et al. in From Sea to Source v2. Protection and Restoration of Fish Migration in Rivers Worldwide (eds Brink, K. et al.) 142–145 (World Fish Migration Foundation, 2018).
Pistocchi, A. et al. Assessment of the Effectiveness of Reported Water Framework Directive Programmes of Measures. Part II—Development of a System of Europe-wide Pressure Indicators. Report No. EUR 28412 EN (Joint Research Centre, 2017).
Garcia de Leaniz, C. Weir removal in salmonid streams: implications, challenges and practicalities. Hydrobiologia 609, 83–96 (2008).
Downward, S. & Skinner, K. Working rivers: the geomorphological legacy of English freshwater mills. Area 37, 138–147 (2005).
Sun, J., Galib, S. M. & Lucas, M. C. Are national barrier inventories fit for stream connectivity restoration needs? A test of two catchments. Wat. Environ. J. https://doi.org/10.1111/wej.12578 (2020).
Atkinson, S. et al. An inspection-based assessment of obstacles to salmon, trout, eel and lamprey migration and river channel connectivity in Ireland. Sci. Total Environ. 719, 137215 (2020).
European Environment Agency European Catchments and Rivers Network System (ECRINS) (EEA, 2012).
Kristensen, P. & Globevnik, L. European small water bodies. Biol. Environ. 114B, 281–287 (2014).
Ferreira, T., Globevnik, L. & Schinegger, R. in Multiple Stressors in River Ecosystems 139–155 (Elsevier, 2019).
Schwarz, U. Hydropower Pressure on European Rivers 36 (WWF, 2019).
Schiemer, F. et al. The Vjosa River corridor: a model of natural hydro-morphodynamics and a hotspot of highly threatened ecosystems of European significance. Land. Ecol. 35, 953–968 (2020).
Duflo, E. & Pande, R. Dams. Q. J. Econ. 122, 601–646 (2007).
Grill, G., Ouellet Dallaire, C., Fluet Chouinard, E., Sindorf, N. & Lehner, B. Development of new indicators to evaluate river fragmentation and flow regulation at large scales: a case study for the Mekong River Basin. Ecol. Indic. 45, 148–159 (2014).
Zarfl, C., Lumsdon, A. E., Berlekamp, J., Tydecks, L. & Tockner, K. A global boom in hydropower dam construction. Aquat. Sci. 77, 161–170 (2015).
Tilt, B., Braun, Y. & He, D. Social impacts of large dam projects: a comparison of international case studies and implications for best practice. J. Environ. Manage. 90, S249–S257 (2009).
Schmitt, R. J. P., Bizzi, S., Castelletti, A. & Kondolf, G. M. Improved trade-offs of hydropower and sand connectivity by strategic dam planning in the Mekong. Nature Sust. 1, 96–104 (2018).
Weibel, D. & Peter, A. Effectiveness of different types of block ramps for fish upstream movement. Aquat. Sci. 75, 251–260 (2013).
Cote, D., Kehler, D. G., Bourne, C. & Wiersma, Y. F. A new measure of longitudinal connectivity for stream networks. Landsc. Ecol. 24, 101–113 (2009).
Tickner, D. et al. Bending the curve of global freshwater biodiversity loss: an emergency recovery plan. BioScience 70, 330–342 (2020).
Bódis, K., Monforti, F. & Szabó, S. Could Europe have more mini hydro sites? A suitability analysis based on continentally harmonized geographical and hydrological data. Renew. Sust. Energy Rev. 37, 794–808 (2014).
Huđek, H., Žganec, K. & Pusch, M. T. A review of hydropower dams in Southeast Europe—distribution, trends and availability of monitoring data using the example of a multinational Danube catchment subarea. Renew. Sust. Energy Rev. 117, 109434 (2020).
European Union Bringing Nature Back Into Our Lives. EU 2030 Biodiversity Strategy. https://eur-lex.europa.eu/legal-content/EN/TXT/?qid=1590574123338&uri=CELEX:52020DC0380 (European Commission, 2020).
Wohl, E. Connectivity in rivers. Progr. Phys. Geog. Earth. Env. 41, 345–362 (2017).
Belletti, B. et al. Datasets for the AMBER Barrier Atlas of Europe. Table S1. Details of test rivers showing number of barriers present in current inventories (Atlas) and those encountered in the field. Table S3. Barrier Database sources. figshare https://doi.org/10.6084/m9.figshare.12629051 (2020).
Jones, J. et al. Quantifying river fragmentation from local to continental scales: data management and modelling methods. Preprint at https://doi.org/10.22541/au.159612917.72148332 (2020).
QGIS Geographic Information System https://qgis.org/en/site/ (Open Source Geospatial Foundation Project, 2010).
Chao, A., Wang, Y. T. & Jost, L. Entropy and the species accumulation curve: a novel entropy estimator via discovery rates of new species. Methods Ecol. Evol. 4, 1091–1100 (2013).
Strahler, A. N. Quantitative analysis of watershed geomorphology. Trans. AGU 38, 913–920 (1957).
R: A Language And Environment For Statistical Computing Version 4.0.0 (2020-04-24) https://www.r-project.org/ (R Foundation for Statistical Computing, 2020).
Signorell, A. et al. DescTools: tools for descriptive statistics. R package version 0.99.37 https://andrisignorell.github.io/DescTools/ (2020).
Januchowski-Hartley, S. R. et al. Restoring aquatic ecosystem connectivity requires expanding inventories of both dams and road crossings. Front. Ecol. Environ. 11, 211–217 (2013).
Schmutz, S. & Moog, O. in Riverine Ecosystem Management 111–127 (Springer, 2018).
European Environment Agency CORINE Land Cover (CLC) Version 20 https://www.eea.europa.eu/data-and-maps/data/copernicus-land-monitoring-service-corine (2012).
European Commission Global Human Settlement—GHS Population Grid https://ghsl.jrc.ec.europa.eu/ghs_pop.php (2015).
European Environment Agency EU-DEM v1.1, https://land.copernicus.eu/imagery-in-situ/eu-dem/eu-dem-v1.1 (Copernicus Land Monitoring Service, 2016).
Meijer, J. R., Huijbregts, M. A. J., Schotten, K. C. G. J. & Schipper, A. M. Global patterns of current and future road infrastructure. Environ. Res. Lett. 13, 064006 (2018).
Louppe, G., Wehenkel, L., Sutera, A. & Geurts, P. in Advances in Neural Information Processing Systems (eds Burges, C. J. C. et al.) 431–439 (Neural Information Processing Systems Foundation, 2013).
National Inventory of Dams http://nid.usace.army.mil/ (2018).
Yoshimura, C., Omura, T., Furumai, H. & Tockner, K. Present state of rivers and streams in Japan. River Res. Appl. 21, 93–112 (2005).
Brazil Dams Safety Report http://www.snisb.gov.br/portal/snisb/relatorio-anual-de-seguranca-de-barragem/2019/rsb19-v0.pdf (National Water Agency (ANA), Brazil, 2020).
World Commission on Dams Dams and Development: A New Framework for Decision Making https://pubs.iied.org/pdfs/9126IIED.pdf (Earthscan Publications, 2000).
International Rivers. The True Cost of Hydropower in China. https://www.internationalrivers.org/wp-content/uploads/sites/86/2020/06/truecostofhydro_en_small.pdf (2014).
Lehner, B., Verdin, K. & Jarvis, A. New global hydrography derived from spaceborne elevation data. Trans. AGU 89, 93–94 (2008).
This study was funded by the EC Horizon 2020 Research and Innovation Programme, AMBER (Adaptive Management of Barriers in European Rivers) Project, grant agreement number 689682, led by C.G.d.L. B.B. was partially supported by EUR H2O’Lyon (ANR-17-EURE-0018) at Université de Lyon. We are indebted to the following institutions, which facilitated barrier data gathering: the International Commission for the Protection of the Danube River (Albania, Croatia, North Macedonia, Serbia, Slovenia); the Ministeri de Medi Ambient, Agricultura i Sostenibilitat. Govern d’Andorra (Andorra); the Bundesministerium für Nachhaltigkeit und Tourismus (Austria); the Service Public de Wallonie, Secrétariat Général (Belgium); the Vlaamse Milieumaatschappij (Belgium); the Agencija za vodno područje Jadranskog mora (Bosnia and Herzegovina); the Balkanka Association (Bulgaria); The Cyprus Conservation Foundation, Terra Cypria (Cyprus); the Ministerstvo Zemědělství (Czech Republic); the Danish Environmental Protection Agency (Denmark); the Keskkonnaministeerium (Estonia); Suomen ympäristökeskus (Finland); the Office national de l’eau et des milieux aquatiques (ONEMA) (France); Landesanstalt für Umwelt Baden-Württemberg (Germany); Bayerisches Landesamt für Umwelt (Germany); Senatsverwaltung für Umwelt, Verkehr und Klimaschutz Berlin (Germany); Landesamt für Umwelt Brandenburg (Germany); Der Senator für Umwelt, Bau und Verkehr Bremen (Germany); Amt für Umweltschutz Hamburg (Germany); Hessisches Landesamt für Naturschutz, Umwelt und Geologie (Germany); Landesamt für Umwelt, Naturschutz und Geologie Mecklenburg-Vorpommern (Germany); Ministerium für Umwelt, Energie, Bauen und Klimaschutz Niedersachsen (Germany); Landesamt für Natur, Umwelt und Verbraucherschutz Nordrhein-Westfalen (Germany); Landesamt für Umwelt Rheinland-Pfalz (Germany); Sächsisches Landesamt für Umwelt, Landwirtschaft und Geologie (Germany); Landesbetrieb für Hochwasserschutz und Wasserwirtschaft Sachsen-Anhalt (Germany); Landesamt für Landwirtschaft, Umwelt und ländliche Räume des Landes Schleswig-Holstein (Germany); Thüringer Landesamt für Umwelt und Geology (Germany); Bundesanstalt für Gewässerkunde (Germany); the Greek Committee on Large Dams (Greece); the WWF Greece; Országos Vízügyi Főigazgatóság (Hungary); the Marine and Freshwater Research Institute (Iceland); Inland Fisheries Ireland (Ireland); Registro Italiano Dighe (Italy); Regione Emilia-Romagna, Lombardia, Piemonte, Toscana (Italy), Latvijas Vides, ģeoloģijas un meteoroloģijas centrs (Latvia); Aplinkos apsaugos agentūra (Lithuania); the Ministère du Développement durable et des Infrastructures (Luxembourg); the Ministarstvo poljoprivrede i ruralnog razvoja (Montenegro); PDOK (The Netherlands); VISpas (The Netherlands); Norges vassdrags-og energidirektorat (Norway); Gospodarstwo Wody Polskie, National Water Management Board (Poland); the Stanisław Sakowicz Inland Fisheries Institute (Poland); the Universidade de Lisboa, Centro de Estudos Florestais (Portugal); Agência Portuguesa do Ambiente (Portugal); Ministerul Apelor și Pădurilor (Romania); WWF Danube-Carpathian (Romania); Ministerstvo životného prostredia (Slovakia); Confederación Hidrográfica del Júcar (Spain); Confederación Hidrográfica del Cantábrico (Spain); Confederación Hidrográfica del Duero (Spain); Confederación Hidrográfica del Tajo (Spain); Confederación Hidrográfica del Guadiana (Spain); Confederación Hidrográfica del Ebro (Spain); Uraren Euskal Agentzia (Spain); Confederación Hidrográfica del Guadalquivir (Spain); Confederación Hidrográfica del Segura (Spain); Universidad de Murcia (Spain); Universidad de Córdoba (Spain); Universidad de Cantabria (Spain); Ministerio para la Transición Ecológica y el Reto Demográfico (Spain); Agència Catalana de l’Aigua (Spain); SUDOANG (Spain); LST Biotopkartering vandringshinder (Sweden); Nationella Biotopkarteringsdatabasen (Sweden); Federal Office for the Environment (FOEN) (Switzerland); Geocat.ch (Switzerland); the Environment Agency (UK); Natural Resources Wales (UK); and the Scottish Environment Protection Agency (UK). We thank G. Luoni for help in developing the random forest regression model, and many students and colleagues who helped with field surveys across Europe.
The authors declare no competing interests.
Peer review information Nature thanks Arnout van Soesbergen, Christiane Zarfl and the other, anonymous, reviewer(s) for their contribution to the peer review of this work. Peer reviewer reports are available.
Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Extended data figures and tables
To correct for under-reporting and derive more accurate estimates of barrier density we used a four-step approach: (1) compilation of georeferenced barrier records from local, regional and national barrier databases (the AMBER Barrier Atlas), (2) data cleaning and removal of duplicate records, (3) ground-truthing barrier densities from walkover river surveys, and (4) statistical barrier modelling via random forest regression.
Extended Data Fig. 2 Cumulative height distribution of artificial barriers found in European rivers.
The figure shows (log10 scale) that most barriers (68% of n = 117,371 built structures equal to or greater than 10 cm in height) are low-head structures (such as fords, culverts and sluice gates) smaller than 2 m in height; these are ubiquitous but typically unreported in existing barrier inventories.
Extended Data Fig. 3 Location of test reaches used to ground-truth the AMBER Barrier Atlas during walkover surveys.
We walked 147 test reaches totalling 2,715 km that were representative of river types found in Europe in terms of altitude, slope, stream order, biogeography and land use. River network and country boundaries were sourced from the European Environment Agency35.
Extended Data Fig. 4 Variation in areal barrier density and main drivers of barrier abundance modelled by random forest regression.
a, The predicted barrier density at ECRINS sub-catchments (barriers per km2; number of sub-catchments 8,467). b, Agricultural pressure (proportion of agricultural area, Corine Land Cover 2, level 1). c, Road crossing density (crossings per km2), d, Mean altitude (m.a.s.l., metres above sea level). e, Extent of surface water (proportion of area occupied by surface water, Corine Land Cover 5, level 1). f, The relative weight (MDI) of the 11 predictors used to model barrier density (detailed in Extended Data Table 4). Country and sub-basin boundaries, CORINE Land Cover and mean altitude were sourced from the European Environment Agency35,61,63 and road density was sourced from the GRIP database64.
The maps show the distribution of modelling residuals (predicted minus observed barrier density, in units of barriers per km2) for the model calibration dataset (number of sub-catchments 2,306) (a), and the whole AMBER Barrier Atlas dataset (number of sub-catchments 8,467) (b). Country and sub-basin boundaries were sourced from the European Environment Agency35.
About this article
Cite this article
Belletti, B., Garcia de Leaniz, C., Jones, J. et al. More than one million barriers fragment Europe’s rivers. Nature 588, 436–441 (2020). https://doi.org/10.1038/s41586-020-3005-2
This article is cited by
Nature Water (2023)
Nature Sustainability (2023)
Freshwater species diversity loss embodied in interprovincial hydroelectricity transmission with ecological network analysis
Environmental Science and Pollution Research (2023)
Truths of the Riverscape: Moving beyond command-and-control to geomorphologically informed nature-based river management
Geoscience Letters (2022)