The spread of artificial barriers across rivers—dams, weirs, and a variety of man-made wall structures—has disrupted the natural dynamics of river channels. A recent regional study estimates about 5,700 such obstacles scattered throughout Spain. These barriers affect sediment movement toward the coast, hinder the migration of native species, and facilitate the spread of nonnative ones. Yet Spain is at the forefront of efforts to remove these blockages, as highlighted by a European study.
In particular, the Dam Removal Progress 2021 report, an annual compilation by several European conservation groups, shows that Spain led the way in removing river obstructions that year.
A total of 108 river-related barriers, structures, and other alterations that changed river systems in 2021 were removed. While this figure is modest when juxtaposed with the broader removals needed, it surpasses the next closest country, Sweden, which dismantled 40 obstacles. France followed with 39, Finland with 16, and the United Kingdom with 10.
The principal elements that disrupt the natural flow of rivers and affect their biomechanics and biodiversity include dams, weirs, and any structure, sometimes accompanied by nearby homes or storage facilities, that interrupts the river’s natural operation.
Among the restorations highlighted in Spain are the dismantling of dams on the Pámanes River in Cantabria and the Oria River in Guipúzcoa in 2021, as well as the removal of the Matabosc embankment along the Ter River.
In 2021, 239 barriers, dams, and obstructions were removed across 17 European countries, marking the highest annual total recorded by the organizations responsible for restoration work.
Removing barriers to restore longitudinal connectivity in rivers is now a notable trend across Europe, according to the report authors. The rapid pace of barrier removals is linked to widespread impacts on natural ecosystems, including altered sediment transport, shifts in flow regimes and temperatures, changes in nutrients, habitat degradation, transformations of aquatic communities, and declines in species abundance.
When a dam, reservoir, or any barrier interrupts river flow, it can impede fish migration and sediment drift toward shores. WWF has repeatedly called for quicker action in managing these barriers to preserve local fish populations, reduce the spread of exotic species, and maintain sediment transfer that supports shoreline and coastal ecosystems.
Over time these structures, once serving roles such as water collection, flood prevention, and resource transfer, degrade with age. They often become obsolete and are abandoned, leaving rivers exposed to negative visual impact and ecological stress.
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