U.S. Fish and Wildlife Service, Partners for Fish and Wildlife biologist Mark Cookson wades through a pond behind a man-made "beaver dam." Prior to the dams construction this area dried annually. It now holds water year round providing refuge for salmon fry. - Photo Credit: AaronMize/USFWS

A man-made dam, constructed from pine logs and willow branches is intended to mimic a beaver dam, slowing and pooling water. - Photo Credit: Aaron Mize/USFWS

A Chinook salmon in the Scott River approaching a man-made beaver dam. This salmon will spawn down-stream of the dam, jump the dam or swim up a side channel around the dam to spawn. With a little luck, it's off-spring will find the deep pool formed by beaver dam where they will spend the summer before swimming to the Pacific Ocean. - Photo Credit: Aaron Mize/USFWS

By Aaron Mize

The Scott River, a tributary of the Klamath River, was originally named “Beaver River” by the Hudson Bay Company trappers who first entered the Scott Valley in the 1830’s beavers were so abundant that one trapper claimed that “Beaver Valley” was “the richest place for beaver he had ever seen. Salmon were also abundant, with large runs of Chinook and coho as well as steelhead trout, lamprey and fresh water mussels. These fish wove their way through and around the maze of beaver dams, their overflows and spills, to spawn in the “Beaver River.”

“The river came by its name honestly,” says Mark Cookson, U.S. Fish and Wildlife Service fisheries biologist with the Partners for Fish and Wildlife Program, in Yreka, Calif.. “There were pretty much continuous beaver made wetlands along the river.”

The Scott River valley has great potential to once again become a significant salmon producer while continuing to support the agricultural throughout the valley. On-the-ground efforts by landowners and others are helping bring this watershed into balance: a balance of beaver and salmon.

Beaver dams, it turns out, have beneficial effects that can’t easily be replicated in other ways. They raise the water table alongside a stream, aiding the growth of trees and plants that stabilize the banks and prevent erosion and improve fish and wildlife habitat, especially salmon habitat. But as Cookson happily points out,  the balance doesn’t end there.  “The higher water table helps agricultural producers, bringing the balance of salmon and beaver into balance with the needs of humans,” he added.

In both Chinook and coho salmon, the eggs incubate in their gravel nests in the river channel throughout the winter, with young “fry” emerging from the gravel in late winter or spring. Upon emergence, these fry require quality rearing habitat to feed and avoid fast water and predation. The deep pools formed by beaver dams are “outstanding rearing habitat for juvenile Chinook and coho salmon,” he said.

While some beaver have returned to the Scott River valley today, many sections of river were channelized during gold mining operations in the early 20th century, leaving the river unsuitable for beaver to begin building their dams. In these areas humans are now building the beaver dams, without immediate help from the beavers. The Scott River Watershed Council has partnered with the U.S. Fish and Wildlife Service, Partners for Fish and Wildlife Program, National Oceanic and Atmospheric Administration, California Department of Fish and Wildlife and Natural Resource Conservation Service to construct a series of six structures, built from pine logs and willow branches that mimic a beaver dam, slowing and pooling water.

Many sections of the river that historically dried up during the summer months will now pool water year-round. The pooling of water, held back by the human made beaver dams, should lead to a cascade of ecological changes. The ponds will provide a haven for the young salmon before they migrate back to the ocean and will nourish young willows and other trees — prime beaver food.

“We hope these structures will give real beavers a chance to move in and maintain the structures we created, to continue providing salmon habitat” Cookson said. “There are a lot of unknowns before we can say what the return of beaver dams will mean for the valley.” 

“The assumption is that by recreating the natural condition, a condition where beaver and salmon co-existed, while additionally balancing the needs of agriculture and people, we will do no harm to the 'Beaver Valley'” he said.

Aaron Mize is the deputy refuge manager for Bosque del Apache National Wildlife Refuge in San Antonio, New Mexico, and is currently completing an Advanced Leadership Development assignment at the Yreka (Calif.) Fish and Wildlife Office.