A few years ago, we wrote an article on the importance of beavers and the dams they create in our waterways. Because beaver dams are so important, we thought it was worth another article.
While breaching beaver dams to help salmon navigate the creeks and rivers seem logical, the dams actually help salmon thrive. When salmon stack up behind a beaver dam, rather than being an impediment to salmon getting upstream to spawn, it is quite the opposite. Salmon stack up behind a beaver dam because there isn’t enough water in the creek yet to provide the right conditions for salmon to successfully spawn upstream. When there is enough water for successful spawning, the water pressure behind the dam will either create a channel through the dam that allows fish to swim through it, or the water will overflow the beaver dam and create a path for the salmon to swim over it. In the latter case, as the salmon crash onto the dam as they swim up, the dam materials become more tightly packed in that area, improving conditions even more for the next salmon. Female salmon will also take turns digging a tunnel through a beaver dam when necessary. The salmon will use the same motion used when digging a redd (nest) to tunnel through the dam. Each subsequent salmon passing through the beaver dam will further enlarge the tunnel.
Salmon and beaver have been successfully coexisting for millennia, so humans don’t need to involve themselves to help the salmon overcome a beaver dam. When humans create holes in beaver dams, it actually harms salmon. The sudden rush of the dammed water gives salmon the false impression that there is a substantial amount of water upstream and encourages them to advance when they should wait instead for better spawning conditions. Salmon moving through a damaged beaver dam arrive at their spawning grounds and spawn in water that is too shallow. When the torrential rains come and the creeks swell, the rushing water scours out the redds (the depressions female salmon make in the gravel to safely deposit their eggs) and washes away the eggs. This scouring becomes even more prevalent during climate-change induced heavy rain events. When salmon wait until the creeks are swollen with water to spawn, they select more stable areas to build their redds and their eggs are more likely to stay put as a result.
The more we understand nature, the better friend we are to it. If you come across a beaver dam on the Preserve or elsewhere, the best thing to do is leave it to nature to resolve salmon passage.
If you’re interested in learning more about salmon and beaver, check out the many resources here, here and here (narrated by Amy Lawrence, Foundation Board member and Professor at Olympic College).
The relationship between salmon and beavers is a wonderful example of natural systems at work. We don’t need to interfere.
– Katha Miller-Winder, President