Beaver and salmonids (trout and salmon) have co-evolved over millennia, so beaver dams typically pose no significant barrier to salmonid movement except during very dry periods. The overall effect of beavers and their dams on salmonids is overwhelming positive, not negative. (See the link below for journal articles).
Scientific researchers have proven that beaver dams improve juvenile salmonid survival and growth. More beaver dams on salmon producing streams result in more and bigger juvenile salmon. Therefore in the Pacific Northwest a critical component of current salmon recovery efforts aims to increase the number of beavers and beaver dams on salmon producing streams.
Unfortunately though, sometimes beavers block road culverts which can obstruct fish passage. Breaching dams, opening culverts and trapping beavers can be difficult, labor intensive and expensive. The most cost-effective, long-term and fish-friendly solution to this problem can be installing a fish-friendly culvert device such as the Snohomish Pond Leveler.
The Snohomish Pond Leveler (SPL) is an innovative flow device that cost-effectively protects road culverts from beaver damming while facilitating adult salmon migration. The SPL has fish-friendly adaptations at both ends of a traditional pond leveler flow device. The prototype in Snohomish County was very successful in assisting adult Coho salmon passage. Further study of this innovative device is needed.
The Snohomish Pond Leveler may make it possible to better manage two Keystone species, beavers and salmon. It promises cost-effective, long-term, salmon passage at beaver damming sites. Rather than trapping beavers and breaking their dams this device may allow more beavers to remain on the landscape to increase both salmon populations and the myriad of species that rely on these two Keystone species for their survival. The Snohomish Pond Leveler is an innovation that with further study and implementation could profoundly improve salmon recovery.