River fragmentation throughout Europe is more prevalent than previously thought, raising concerns for biodiversity and the provision of ecosystem services. More than 1.2 million barriers, from large-scale dams to locks to weirs, stretch across rivers on the continent, more than twice as many as previously thought, according to an international research project.

To conduct a detailed survey of rivers in 36 European countries, scientists first examined more than 120 databases of river infrastructure throughout 1.65 million km of rivers in Europe. Realizing that structures less than two meters in height were not included in the datasets, the researchers took an extended field trip and Source: Barbara Belletti et al.walked along 2,715 km of rivers to complete the barrier infrastructure inventory.

The rivers were observed to average one barrier every 0.6 km, with densities ranging from five barriers per 1,000 km in Montenegro to almost 20 barriers per kilometer in the Netherlands, making Europe’s waterways possibly the most fragmented river network in the world. Large-scale projects, classified as 15 m or higher, account for less than 1% of the barriers on European rivers. More than 90% of blockages are under 5 m tall.

Barriers of all sizes disrupt the transport and delivery of sediments and nutrients, as well as the migration and dispersal of aquatic organisms. The study could inform the implementation of the EU Biodiversity Strategy formulated to reconnect 25,000 km of Europe’s rivers by 2030.

The researchers are affiliated with University of Lyon (France), Swansea University (U.K.), University of Padova (Italy), Conservatoire National du Saumon Sauvage (France), Politecnico di Milano (Italy), Technical University of Denmark, European Commission Joint Research Centre (Italy), Inland Fisheries Ireland, Polish Academy of Sciences, World Fish Migration Foundation (The Netherlands), Italian National Institute for Environmental Protection and Research, Leibniz Institute of Freshwater Ecology and Inland Fisheries (Germany), University of Oviedo (Spain), Ingenieurbüro kauppert (Germany), AEMS-Rios con Vida (Spain), Oregon State University, Durham University (U.K.), University of Southampton (U.K.), University of Highlands and Islands (U.K.), University College Cork (Ireland), University of Kent (U.K.), Stanisław Sakowicz Inland Fisheries Institute (Poland), Polytechnic University of Madrid, The Nature Conservancy (Maine), RWE Generation SE (Germany), University of Strasbourg (France) and Princeton Hydro (Connecticut).