Overview
The removal of human-made barriers, such as dams and weirs, from rivers is a method used to restore natural water flow and sediment transport. This practice is primarily aimed at allowing aquatic wildlife, including fish, to move more freely within river systems. While barrier removal facilitates the movement of native species, it also creates potential pathways for invasive species to spread, which can impact conservation outcomes.
Research Context
Approximately one-quarter of all freshwater species globally face a threat of extinction. The removal of human-made river barriers is a popular approach in river restoration efforts. These efforts aim to revert river conditions to a more natural state, which typically involves restoring hydrological connectivity and sediment dynamics. The unrestricted movement of aquatic organisms is a key benefit cited for dam removal.
Findings
The removal of dams and weirs enables the unimpeded movement of river wildlife. This increased connectivity, while beneficial for native species, also permits the movement and potential spread of invasive species. This dual effect presents a challenge in dam removal projects, as the benefits of restoring natural flow and native species mobility must be weighed against the risk of facilitating invasive species expansion.
Why This Matters
The dual impact of dam removal — enabling both native and invasive species movement — complicates river conservation strategies. Understanding these dynamics is crucial for designing effective restoration projects that maximize benefits for threatened freshwater species while mitigating the risks posed by invasive species. The choice of river restoration methods, particularly barrier removal, has implications for managing biodiversity in freshwater ecosystems.