Oregon Sea Grant

More than one million barriers fragment Europe's rivers

Abstract: Rivers support some of Earth’s richest biodiversity and provide essential ecosystem services to society, but they are often fragmented by barriers to free flow. 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 kilometer),
68 percent of which are structures less than two metres in height that are often overlooked. Standardized walkover surveys along 2,715 kilometers of stream length for 147 rivers indicate that existing records underestimate barrier numbers by about 61 percent. 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, the density of river-road crossings, the 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 kilometers 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.

Authors: Barbara Belletti, Carlos Garcia de Leaniz, Joshua Jones, Simone Bizzi, Luca Börger, Gilles Segura, Andrea Castelletti, Wouter van de Bund, Kim Aarestrup, James Barry,Kamila Belka , Arjan Berkhuysen, Kim Birnie-Gauvin, Martina Bussettini, Mauro Carolli,Sofia Consuegra, Eduardo Dopico, Tim Feierfeil, Sara Fernández, Pao Fernandez Garrido,Eva Garcia-Vazquez, Sara Garrido, Guillermo Giannico, Peter Gough, Niels Jepsen, Peter E. Jones, Paul Kemp, Jim Kerr, James King, Małgorzata Łapińska, Gloria Lázaro, Martyn C. Lucas, Lucio Marcello, Patrick Martin, Phillip McGinnity, Jesse O’Hanley, Rosa Olivo del Amo, Piotr Parasiewicz, Martin Pusch, Gonzalo Rincon, Cesar Rodriguez, Joshua Royte, Claus Till Schneider, Jeroen S. Tummers, Sergio Vallesi, Andrew Vowles, Eric Verspoor, Herman Wanningen, Karl M. Wantzen, Laura Wildman, Maciej Zalewski