More Than 1 Million Barriers Are Blocking Europe’s Rivers

The 440-foot-high El Atazar Dam near Madrid, Spain.

The 440-foot-high El Atazar Dam near Madrid, Spain. Carlos Delgado / Wikimedia Commons

More than 1.2 million barriers stretch across rivers in Europe, from large-scale dams to locks to weirs — more than twice as many as previously thought, according to new research published in the journal Nature. Scientists said the artificial structures threaten some of the world’s most diverse ecosystems.

“The extent of river fragmentation in Europe is much higher than anyone had anticipated,” Barbara Belletti, a river geomorphologist at Politecnico di Milano who led the study, said in a statement.

The research presents the most detailed survey of rivers in 36 European countries to date. Scientists first examined more than 120 databases of river infrastructure in Europe. Most databases, they found, only included barriers over a certain height. So the researchers went into the field, walking along more than 1,677 miles of European rivers to document any structures that may have been missed.

The study concluded that Europe’s rivers average one barrier every 0.6 kilometers, with densities ranging from five barriers per 1,000 kilometers in Montenegro to almost 20 barriers per kilometer in the Netherlands. The estimated 1.2 million barriers make Europe’s waterways possibly the most fragmented river network in the world.

While officials and conservationists are most vocal in their concerns about hydroelectric dams, the research found large-scale projects, classified as 50 feet or higher, account for less than 1 percent of the barriers on European rivers. More than 90 percent of blockages are under 16 feet tall. Barriers of all sizes disrupt the transport and delivery of sediments and nutrients, as well as the migration and dispersal of aquatic organisms.

“To avoid ‘death by a thousand cuts,’ a paradigm shift is necessary: to recognize that although large dams may draw most of the attention, it is the small barriers that collectively do most of the damage,” the scientists wrote. “Small is not beautiful.”