Tuesday June 9, 2026
The Conversation —
Almost a quarter of all freshwater species are threatened with extinction. The removal of human-made barriers from rivers, such as dams and weirs, is a popular way to restore water flow and sediment transport to its natural state and allow fish and other aquatic wildlife to move more freely.
There are more than 1.2 million barriers in European rivers. But more than 2,200 dams, weirs and other barriers have been removed between 2020 and 2025.
This may help native species move more freely, but we’ve been researching how non-native invasive species respond to the removal of barriers along rivers.
In a new study, our team analysed data from 45 studies that monitored freshwater communities before and after river barriers were removed. We found that native species generally benefited from barrier removal and showed stronger long-term recovery than invasive species. However, invasive freshwater invertebrates increased substantially following removal, suggesting that reconnecting rivers can also have unintended consequences.
Our paper highlights what conservation scientists increasingly call the “connectivity conundrum”, where restoring connectivity can benefit native biodiversity while simultaneously increasing invasion risk.