Artificial beaver dams built in northern California are recreating lost wetlands and boosting threatened coho salmon survival, with results described as “mind blowing” by fish biologist Michael Pollock of NOAA’s Northwest Fisheries Science Center.

The Scott River valley, once known as Beaver Valley, lost thousands of beavers to European fur trappers in the 1830s, diminishing the cold, slow-moving habitat favored by coho salmon. In 2015, the Scott River Watershed Council built two artificial dams on Sugar Creek, followed by more on French Creek. Beavers sometimes repaired and expanded these structures, improving their quality.

These low-cost dams created about 9,000 square metres of new habitat, supporting over 8,500 young salmon. Juvenile coho survival rates soared from 8% before the dams were built to 60% afterwards. Salmon returns to the Scott River remained healthy even during severe drought, outperforming other monitored rivers.

Pollock notes the dams remind people of the beaver's ecological importance, but beavers can only thrive if landowners allow them. The findings are published in Frontiers in Ecology and Evolution.