Free-flowing rivers (FFRs) support diverse, complex and dynamic ecosystems globally, providing important societal and economic services. Infrastructure development threatens the ecosystem processes, biodiversity and services that these rivers support. Here we assess the connectivity status of 12 million kilometres of rivers globally and identify those that remain free-flowing in their entire length. Only 37 per cent of rivers longer than 1,000 kilometres remain free-flowing over their entire length and 23 per cent flow uninterrupted to the ocean. Very long FFRs are largely restricted to remote regions of the Arctic and of the Amazon and Congo basins. In densely populated areas only few very long rivers remain free-flowing, such as the Irrawaddy and Salween. Dams and reservoirs and their up- and downstream propagation of fragmentation and flow regulation are the leading contributors to the loss of river connectivity. By applying a new method to quantify riverine connectivity and map FFRs, we provide a foundation for concerted global and national strategies to maintain or restore them.
Access optionsAccess options
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.
Rent or Buy article
Get time limited or full article access on ReadCube.
All prices are NET prices.
The geometric dataset of the global river network and the associated attribute information for every river reach—that is, the values of all pressure indicators (DOF, DOR, SED, USE, RDD and URB)—as well as the main results of the study—that is, values for the CSI, the dominant pressure factor and the FFR status— are available at https://doi.org/10.6084/m9.figshare.7688801 under a CC-BY-4.0 license. The dataset can be used together with the published source code (see ‘Code availability’) to recalculate the main study results and to run existing and new scenarios. The databases of dams required to calculate the DOF, DOR and SED indicators are not in the data repository owing to licensing issues, but are freely available at http://www.globaldamwatch.org. Original data that supported the study—that is, raw datasets of roads, urban areas, water use, waterfalls, erosion data and floodplain information—and their sources are summarized in Extended Data Table 1. Additional higher-resolution maps of Figs. 1–3 are available at http://www.hydrolab.io/ffr.
The source code of the main tools, scripts and algorithms used in this research is available under the GNU General Public License v3.0 at https://github.com/ggrill/Free-Flowing-Rivers. Other procedures and GIS steps (as described in Methods) were conducted manually and are therefore not part of the code repository.
Ripl, W. Water: the bloodstream of the biosphere. Philos. Trans. R. Soc. B. 358, 1921–1934 (2003).
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).
Nilsson, C. et al. Forecasting environmental responses to restoration of rivers used as log floatways: an interdisciplinary challenge. Ecosystems 8, 779–800 (2005).
Revenga, C., Brunner, J., Henninger, N., Kassem, K. & Payne, R. Freshwater Systems. Report No. 1569734607 (World Resources Institute, 2000).
Dudgeon, D. et al. Freshwater biodiversity: importance, threats, status and conservation challenges. Biol. Rev. Camb. Philos. Soc. 81, 163–182 (2006).
Cardinale, B. J. et al. Biodiversity loss and its impact on humanity. Nature 486, 59–67 (2012); corrigendum 489, 326 (2012).
Ward, J. V. & Stanford, J. A. The serial discontinuity concept: extending the model to floodplain rivers. Regul. Rivers Res. Manage. 10, 159–168 (1995).
Ward, J. V. The four-dimensional nature of lotic ecosystems. J. N. Am. Benthol. Soc. 8, 2 (1989).
Poff, N. L. et al. The natural flow regime: a paradigm for river conservation and restoration. Bioscience 47, 769–784 (1997).
Pringle, C. M. What is hydrologic connectivity and why is it ecologically important? Hydrol. Processes 17, 2685–2689 (2003).
Nilsson, C. & Berggren, K. Alterations of riparian ecosystems caused by river regulation. Bioscience 50, 783–792 (2000).
Olden, J. D. in Conservation of Freshwater Fishes: Challenges and Opportunities for Fish Conservation in Dam-impacted Waters (eds Closs, G. P. et al.) 107–148 (Cambridge Univ. Press, Cambridge, 2016).
Costanza, R. et al. The value of the world’s ecosystem services and natural capital. Nature 387, 253–260 (1997).
Opperman, J. J., Moyle, P. B., Larsen, E. W., Florsheim, J. L. & Manfree, A. D. Floodplains: Processes and Management for Ecosystem Services (Univ. California Press, Oakland, 2017).
Benchimol, M. & Peres, C. A. Widespread forest vertebrate extinctions induced by a mega hydroelectric dam in lowland Amazonia. PLoS One 10, e0129818 (2015).
Lees, A. C., Peres, C. A., Fearnside, P. M., Schneider, M. & Zuanon, J. A. S. Hydropower and the future of Amazonian biodiversity. Biodivers. Conserv. 25, 451–466 (2016).
Vörösmarty, C. J. et al. Global threats to human water security and river biodiversity. Nature 467, 555–561 (2010).
Syvitski, J. P. M. et al. Sinking deltas due to human activities. Nat. Geosci. 2, 681–686 (2009).
McIntyre, P. B., Reidy Liermann, C. A. & Revenga, C. Linking freshwater fishery management to global food security and biodiversity conservation. Proc. Natl Acad. Sci. USA 113, 12880–12885 (2016).
Auerbach, D. A., Deisenroth, D. B., McShane, R. R., McCluney, K. E. & Poff, N. L. Beyond the concrete: accounting for ecosystem services from free-flowing rivers. Ecosyst. Serv. 10, 1–5 (2014).
Arthington, A. H. et al. The Brisbane declaration and global action agenda on environmental flows (2018). Front. Environ. Sci. 6 45 (2018).
Zarfl, C., Lumsdon, A. E., Berlekamp, J., Tydecks, L. & Tockner, K. A global boom in hydropower dam construction. Aquat. Sci. 77, 161–170 (2015).
Adams, K. et al. 2017 Hydropower Status Report (International Hydropower Association, 2017); https://www.hydropower.org/sites/default/files/publications-docs/2017HydropowerStatusReport.pdf.
Winemiller, K. O. et al. Balancing hydropower and biodiversity in the Amazon, Congo, and Mekong. Science 351, 128–129 (2016).
Shumilova, O., Tockner, K., Thieme, M., Koska, A. & Zarfl, C. Global water transfer megaprojects: a potential solution for the water-food-energy nexus? Front. Environ. Sci. 6, 150 (2018).
Grill, G. et al. An index-based framework for assessing patterns and trends in river fragmentation and flow regulation by global dams at multiple scales. Environ. Res. Lett. 10, 015001 (2015).
Nilsson, C., Reidy, C. A., Dynesius, M. & Revenga, C. Fragmentation and flow regulation of the world’s large river systems. Science 308, 405–408 (2005).
Reidy Liermann, C., Nilsson, C., Robertson, J. & Ng, R. Y. Implications of dam obstruction for global freshwater fish diversity. Bioscience 62, 539–548 (2012).
Lehner, B. & Grill, G. Global river hydrography and network routing: baseline data and new approaches to study the world’s large river systems. Hydrol. Processes 27, 2171–2186 (2013).
Palmer, M. A. et al. Climate change and the world’s river basins: anticipating management options. Front. Ecol. Environ. 6, 81–89 (2008).
Lehner, B., Verdin, K. & Jarvis, A. New global hydrography derived from spaceborne elevation data. Eos 89, 93 (2008).
Mulligan, M., Saenz-Cruz, L., van Soesbergen, A., Smith, V. T. & Zurita, L. Global dam database and Geowiki, version 1 http://globaldamwatch.org/ (2009).
Couto, T. B. A. & Olden, J. D. Global proliferation of small hydropower plants: science and policy. Front. Ecol. Environ. 16, 91–100 (2018).
Karr, J. Biological integrity: a long neglected aspect of water resource management. Ecol. Appl. 1, 66–84 (1991).
Poff, N. L. Landscape filters and species traits: towards mechanistic understanding and prediction in stream ecology. J. N. Am. Benthol. Soc. 16, 391–409 (1997).
Kuehne, L. M., Olden, J. D., Strecker, A. L., Lawler, J. J. & Theobald, D. M. Past, present, and future of ecological integrity assessment for fresh waters. Front. Ecol. Environ. 15, 197–205 (2017).
Zhuang, W. Eco-environmental impact of inter-basin water transfer projects: a review. Environ. Sci. Pollut. Res. Int. 23, 12867–12879 (2016).
Gallardo, B. & Aldridge, D. C. Inter-basin water transfers and the expansion of aquatic invasive species. Water Res. 143, 282–291 (2018).
Bartley, D. M., De Graaf, G. J., Valbo-Jorgensen, J. & Marmulla, G. Inland capture fisheries: status and data issues. Fish. Manag. Ecol. 22, 71–77 (2015).
Ziv, G., Baran, E., Nam, S., Rodríguez-Iturbe, I. & Levin, S. A. Trading-off fish biodiversity, food security, and hydropower in the Mekong River Basin. Proc. Natl Acad. Sci. USA 109, 5609–5614 (2012).
Schmitt, R. J., Bizzi, S., Castelletti, A. & Kondolf, G. Improved trade-offs of hydropower and sand connectivity by strategic dam planning in the Mekong. Nat. Sustainability 1, 96–104 (2018).
US Energy Information Administration. International Energy Outlook. Report No. DOE/EIA-0484 (US Energy Information Administration, 2016).
Opperman, J., Grill, G. & Hartmann, J. The Power of Rivers: Finding Balance Between Energy and Conservation in Hydropower Development (The Nature Conservancy, Washington, DC, 2015).
Jägermeyr, J., Pastor, A., Biemans, H. & Gerten, D. Reconciling irrigated food production with environmental flows for Sustainable Development Goals implementation. Nat. Commun. 8, 15900 (2017).
Palmer, M. A., Hondula, K. L. & Koch, B. J. Ecological restoration of streams and rivers: shifting strategies and shifting goals. Annu. Rev. Ecol. Evol. Syst. 45, 247–269 (2014).
Magilligan, F. J. et al. River restoration by dam removal: enhancing connectivity at watershed scales. Elem. Sci. Anth. 4, 000108 (2016).
Kemp, P. S. & O’Hanley, J. R. Procedures for evaluating and prioritising the removal of fish passage barriers: a synthesis. Fish. Manag. Ecol. 17, 297–322 (2010).
Sheer, M. B. & Steel, E. A. Lost watersheds: barriers, aquatic habitat connectivity, and salmon persistence in the Willamette and Lower Columbia River basins. Trans. Am. Fisheries Soc. 135, 1654–1669 (2006).
Groves, C. R. et al. Incorporating climate change into systematic conservation planning. Biodivers. Conserv. 21, 1651–1671 (2012).
UN Water Integrated Monitoring Guide for SDG 6 (UN Water, 2017); http://www.unwater.org/publications/integrated-monitoring-guide-sdg-6.
WWF. Free-Flowing Rivers: Economic Luxury or Ecological Necessity? (WWF, Gland, 2006).
Döll, P., Kaspar, F. & Lehner, B. A global hydrological model for deriving water availability indicators: model tuning and validation. J. Hydrol. 270, 105–134 (2003).
Alcamo, J. et al. Development and testing of the WaterGAP 2 global model of water use and availability. Hydrol. Sci. J. 48, 317–337 (2003).
River discharge data. Global Runoff Data Centre, Federal Institute of Hydrology, Koblenz, Germany https://www.bafg.de/GRDC (2014).
Armstrong, J. S. in Long-range Forecasting: From Crystal Ball to Computer 2nd edn, 346–354 (Wiley, New York, 1985).
Kruk, A. & Penczak, T. Impoundment impact on populations of facultative riverine fish. Ann. Limnol. Int. J. Lim. 39, 197–210 (2003).
Herbert, M. E. & Gelwick, F. P. Spatial variation of headwater fish assemblages explained by hydrologic variability and upstream effects of impoundment. Copeia 2003, 273–284 (2003).
Ponton, D. & Copp, G. H. Early dry-season community structure and habitat use of young fish in tributaries of the River Sinnamary (French Guiana, South America) before and after hydrodam operation. Environ. Biol. Fishes 50, 235–256 (1997).
Reyes-Gavilán, F., Garrido, R., Nicieza, A., Toledo, M. & Brana, F. Fish community variation along physical gradients in short streams of northern Spain and the disruptive effect of dams. Hydrobiologia 321, 155–163 (1996).
Pracheil, B. M., McIntyre, P. B. & Lyons, J. D. Enhancing conservation of large-river biodiversity by accounting for tributaries. Front. Ecol. Environ. 11, 124–128 (2013).
Messager, M. L., Lehner, B., Grill, G., Nedeva, I. & Schmitt, O. Estimating the volume and age of water stored in global lakes using a geo-statistical approach. Nat. Commun. 7, 13603 (2016).
Lehner, B., Ariwi, J. & Grill, G. HydroFALLS: a global waterfall database. http://wp.geog.mcgill.ca/hydrolab/ (2016).
Dynesius, M. & Nilsson, C. Fragmentation and flow regulation of river systems in the northern third of the world. Science 266, 753–762 (1994).
Constantine, J. A., Dunne, T., Ahmed, J., Legleiter, C. & Lazarus, E. D. Sediment supply as a driver of river meandering and floodplain evolution in the Amazon Basin. Nat. Geosci. 7, 899–903 (2014).
Harvey, A. M. The influence of sediment supply on the channel morphology of upland streams: Howgill Fells, Northwest England. Earth Surf. Process. Landf. 16, 675–684 (1991).
Vörösmarty, C. J. et al. Anthropogenic sediment retention: major global impact from registered river impoundments. Global Planet. Change 39, 169–190 (2003).
Petts, G. E. & Gurnell, A. Dams and geomorphology: research progress and future directions. Geomorphology 71, 27–47 (2005).
Schmitt, R. J. P., Rubin, Z. & Kondolf, G. M. Losing ground – scenarios of land loss as consequence of shifting sediment budgets in the Mekong Delta. Geomorphology 294, 58–69 (2017).
Rubin, Z. K., Kondolf, G. M. & Carling, P. A. Anticipated geomorphic impacts from Mekong basin dam construction. Int. J. River Basin Manage. 13, 105–121 (2015).
Latrubesse, E. M. et al. Damming the rivers of the Amazon basin. Nature 546, 363–369 (2017).
Kondolf, G. M. et al. Changing sediment budget of the Mekong: cumulative threats and management strategies for a large river basin. Sci. Total Environ. 625, 114–134 (2018).
Turowski, J. M., Rickenmann, D. & Dadson, S. J. The partitioning of the total sediment load of a river into suspended load and bedload: a review of empirical data. Sedimentology 57, 1126–1146 (2010).
Borrelli, P. et al. An assessment of the global impact of 21st century land use change on soil erosion. Nat. Commun. 8, 2013 (2017).
Brune, G. M. Trap efficiency of reservoirs. Trans. Am. Geophys. Union 34, 407 (1953).
Morris, G. L. & Fan, J. Reservoir Sedimentation Handbook: Design and Management of Dams, Reservoirs, and Watersheds for Sustainable Use (McGraw-Hill, New York, 1998).
Kummu, M., Lu, X. X., Wang, J. J. & Varis, O. Basin-wide sediment trapping efficiency of emerging reservoirs along the Mekong. Geomorphology 119, 181–197 (2010).
Meybeck, M., Laroche, L., Dürr, H. H. & Syvitski, J. P. M. Global variability of daily total suspended solids and their fluxes in rivers. Global Planet. Change 39, 65–93 (2003).
Milliman, J. D. & Farnsworth, K. L. River Discharge to the Coastal Ocean: A Global Synthesis (Cambridge Univ. Press, Cambridge, 2013).
Vanmaercke, M., Poesen, J., Broeckx, J. & Nyssen, J. Sediment yield in Africa. Earth Sci. Rev. 136, 350–368 (2014).
Guo, L. C., Su, N., Zhu, C. Y. & He, Q. How have the river discharges and sediment loads changed in the Changjiang River basin downstream of the Three Gorges Dam? J. Hydrol. 560, 259–274 (2018).
Yang, H. F. et al. Human impacts on sediment in the Yangtze River: a review and new perspectives. Global Planet. Change 162, 8–17 (2018).
Wang, Y., Rhoads, B. L., Wang, D., Wu, J. & Zhang, X. Impacts of large dams on the complexity of suspended sediment dynamics in the Yangtze River. J. Hydrol. 558, 184–195 (2018).
Dang, T. H. et al. Long-term monitoring (1960–2008) of the river-sediment transport in the Red River Watershed (Vietnam): temporal variability and dam-reservoir impact. Sci. Total Environ. 408, 4654–4664 (2010).
Fan, H., He, D. & Wang, H. Environmental consequences of damming the mainstream Lancang–Mekong River: a review. Earth Sci. Rev. 146, 77–91 (2015).
Fu, K. D., He, D. M. & Lu, X. X. Sedimentation in the Manwan reservoir in the Upper Mekong and its downstream impacts. Quat. Int. 186, 91–99 (2008).
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).
Tessler, Z. D., Vorosmarty, C., Grossberg, M., Gladkova, I. & Aizenman, H. A global empirical typology of anthropogenic drivers of environmental change in deltas. Sustain. Sci. 11, 525–537 (2016).
Wang, L., Lyons, J., Kanehl, P. & Bannerman, R. Impacts of urbanization on stream habitat and fish across multiple spatial scales. Environ. Manage. 28, 255–266 (2001).
Booth, D. B. & Jackson, C. R. Urbanization of aquatic systems: degradation thresholds, stormwater detection, and the limits of mitigation. J. Am. Water Resour. Assoc. 33, 1077–1090 (1997).
Grimm, N. B. et al. Global change and the ecology of cities. Science 319, 756–760 (2008).
Doll, C. N. CIESIN thematic guide to night-time light remote sensing and its applications http://ngdc.noaa.gov/eog/dmsp/downloadV4composites.html#AXP (2008).
Henderson, J. V., Storeygard, A. & Weil, D. N. Measuring economic growth from outer space. Am. Econ. Rev. 102, 994–1028 (2012).
Small, C., Pozzi, F. & Elvidge, C. D. Spatial analysis of global urban extent from DMSP-OLS night lights. Remote Sens. Environ. 96, 277–291 (2005).
Schneider, A., Friedl, M. A. & Potere, D. A new map of global urban extent from MODIS satellite data. Environ. Res. Lett. 4, 044003 (2009).
Fluet-Chouinard, E., Lehner, B., Rebelo, L. M., Papa, F. & Hamilton, S. K. Development of a global inundation map at high spatial resolution from topographic downscaling of coarse-scale remote sensing data. Remote Sens. Environ. 158, 348–361 (2015).
Richter, B. D. et al. Lost in development’s shadow: the downstream human consequences of dams. Water Altern. 3, 14–42 (2010).
Nilsson, C. & Jansson, R. Floristic differences between riparian corridors of regulated and free-flowing boreal rivers. Regul. Riv. Res. Manage. 11, 55–66 (1995).
Gupta, H., Kao, S.-J. & Dai, M. The role of mega dams in reducing sediment fluxes: a case study of large Asian rivers. J. Hydrol. 464–465, 447–458 (2012).
Vörösmarty, C. J., Douglas, E. M., Green, P. A. & Revenga, C. Geospatial indicators of emerging water stress: an application to Africa. Ambio 34, 230–236 (2005).
Smakhtin, V., Revenga, C. & Döll, P. A pilot global assessment of environmental water requirements and scarcity. Water Int. 29, 307–317 (2004).
Pastor, A. V., Ludwig, F., Biemans, H., Hoff, H. & Kabat, P. Accounting for environmental flow requirements in global water assessments. Hydrol. Earth Syst. Sci. 18, 5041–5059 (2014).
Brauman, K. A., Richter, B. D., Postel, S., Malsy, M. & Flörke, M. Water depletion: an improved metric for incorporating seasonal and dry-year water scarcity into water risk assessments. Elem. Sci. Anth. 4, 000083 (2016).
Blanton, P. & Marcus, W. A. Railroads, roads and lateral disconnection in the river landscapes of the continental United States. Geomorphology 112, 212–227 (2009).
Shuster, W. D., Bonta, J., Thurston, H., Warnemuende, E. & Smith, D. R. Impacts of impervious surface on watershed hydrology: a review. Urban Water J. 2, 263–275 (2005).
Schueler, T. R., Fraley-McNeal, L. & Cappiella, K. Is impervious cover still important? Review of recent research. J. Hydrol. Eng. 14, 309–315 (2009).
Funding for this study was provided in part by World Wildlife Fund (WWF), the Natural Sciences and Engineering Research Council of Canada (NSERC Discovery Grant RGPIN/341992-2013) and McGill University, Montreal, Québec, Canada.
Nature thanks Edward Park, N. LeRoy Poff and the other anonymous reviewer(s) for their contribution to the peer review of this work.
The authors declare no competing interests.
Publisher’s note: Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Extended data figures and tables
Methodological steps to define and assess the CSI of individual river reaches (steps 1–5) and decision tree used to assess the free-flowing status of entire rivers (step 6 and following).
a–c, The baseline river network consists of individual ‘river reaches’ (1–32 in a), defined as line segments separated by confluences (black dots). River reaches can be aggregated into ‘rivers’ according to a ‘backbone’ ordering system, which classifies river reaches as the mainstem or a tributary of various higher orders (b). Following this system, the river network can be distinguished into distinct rivers (1–16 in c), defined as contiguous stretches of river reaches from source to outlet on the mainstem or from source to confluence with the next-order river. d, CSI values for individual river reaches, as calculated with our model. If a value is at or above the CSI threshold (95%), the river reach is declared to have good connectivity status; if it is below the threshold, it is declared to be impacted. e, If an entire river (as defined in c) has good connectivity status, it is defined to be an FFR (blue). A river can be partly above the CSI threshold, and thus contiguous stretches can have good connectivity status (green).
a, b, The DOF index ranges from 0% (no fragmentation impact) to 100% (completely fragmented) and is shown for the conceptual approach (a) and the river example (b) in the colour coding shown in b. It is calculated for all river reaches connected to the barrier location in both the up- and downstream directions (but tributaries to the mainstem downstream of the barrier are not considered affected). The impact is largest in connected river reaches that are similar in discharge to the barrier site and diminishes as rivers become increasingly dissimilar in size, that is, larger in the downstream or smaller in the upstream direction. c, DOF decay functions, as considered and evaluated by the expert group.
The SED ranges from 0% to 100%, assessing the degree to which sediment connectivity in any river reach is altered by upstream dams. a, River network with individual river reaches and PSL ranges. b, The SED, which accounts for the relative contribution of tributaries to the total sediment budget of the river network, and its changes in response to changes in longitudinal sediment connectivity.
a–f, Individual indicators within their range of occurrence, between 0% and 100%. The colour schemes are nonlinear and vary between indicators. The blue shades represent the magnitude of river discharge for river reaches with pressure values of 0% (that is, darker shades for larger rivers).
a, Averaged CSI standard deviations for CSI ranges. b, Number of benchmark FFRs correctly classified at different CSI thresholds.
Supplementary Table 1: List of free-flowing rivers longer than 500 km by continent.
Supplementary Table 2: List of reference rivers evaluated for benchmarking. Sources: ‘Expert nominated’ (BENCH_SCR = ‘EXP’) and Nilsson et al.27 (BENCH_SCR = ‘NLS’).
Supplementary Table 3: Results of benchmarking and key statistics of 100 scenarios.
About this article