Restoring connectivity in freshwater ecosystems is widely recognized as a critical strategy for supporting native fish populations and overall aquatic biodiversity. Across North America and beyond, dams and other water barriers are increasingly being removed or modified to reconnect fragmented river networks. While these actions often benefit native species, they also raise a persistent concern: improved connectivity can unintentionally accelerate the spread of invasive species.
Arkilanian, A., Coté, D., Wiersma, Y.F. and Pither, R. 2026. An integrated approach to balance freshwater connectivity restoration and invasion risk. Conservation Biology: e70215. DOI: 10.1111/cobi.70215.
This trade-off is especially pronounced in freshwater systems, where barriers that block native movement may simultaneously limit invasive dispersal. Removing those barriers can therefore expose upstream habitats to new invasion risks. Reconciling the need to restore connectivity for native species while minimizing the spread of invasive species has become a central challenge in freshwater conservation and habitat restoration.
Recent research tackles this problem using the round goby, a highly successful invasive fish that has spread throughout the Great Lakes and many connected river systems. Focusing on the Grand River watershed in southern Ontario, researchers developed an integrated framework that evaluates both native and invasive connectivity at the same time.
The study quantified connectivity for native fish alongside two distinct invasion pathways for round goby: spread from populations already established within the watershed and introductions from Lake Erie at the watershed outlet. The researchers then simulated barrier removals to examine how different restoration strategies affected both native and invasive connectivity.
The results showed that restoring connectivity through barrier removal almost always increased opportunities for invasive spread. In many cases, gains in native connectivity from removing a single barrier were nearly matched by gains in invasive connectivity, particularly because round goby populations were already established in central parts of the river network.
Barriers near the watershed outlet played an outsized role, as their removal could dramatically increase access for invasive species from outside the system. Even when restoration strategies explicitly considered invasive risk, increases in invasive connectivity were difficult to avoid once invasions were well established.
Despite these constraints, the analysis also revealed opportunities for more strategic restoration. By identifying river segments where native connectivity gains were high relative to invasive connectivity, the framework highlighted locations where restoration actions are more likely to benefit native species without substantially increasing invasion risk. These areas may be strong candidates for targeted barrier removal, habitat restoration, or complementary management actions such as selective fish passage or invasive species control.
Overall, this research demonstrates that freshwater connectivity restoration cannot be planned effectively by considering barriers and invasive species separately. An integrated approach that accounts for multiple invasion pathways provides a more realistic basis for decision-making and improves the chances that restoration efforts will achieve long-term conservation gains rather than unintended ecological costs.
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