Written by Reuven Walder - Watershed Biologist for the Salmon Protection and Watershed Network (SPAWN)

One day last March I received a phone call from a Lagunitas resident alerting me to possible creek pollution on the San Geronimo Creek behind his house. When I arrived at Matt's house, the problem could not be detected nor was there any sign of disturbance upstream, but Matt excitedly wanted to show me the large two-foot long steelhead holding in a pool behind his house. He said it had been there for days and he had been watching it constantly.

As I sat on the bank and admired the beautiful fish with him, I noticed that a large leafy branch of a bay tree had fallen into the water on the downstream edge of the pool. It rested partly in the pool and partly over the riffle downstream. Curiously, I asked him, "Are you going to leave that branch in the creek?". "No" he said, "I am going to remove that thing. It's a mess and a fire hazard in the summer."

Of course this was my moment to explain to him how important woody debris (fallen trees or branches) are to the salmonids in the creek ecosystem. Woody debris is extremely important habitat as it can provide cover for juvenile salmonids, create deep pools and attract invertebrates such various aquatic flies, important food sources. In addition, fallen trees create diverse habitat, shade the creek and divert water to form pools, riffles and runs potentially improving spawning habitat for adults and rearing habitat for juveniles. Woody debris can also slow water velocity limiting excessive streambed scour and bank erosion. After our discussion, I left his house feeling convinced that while he heard my words, he was still going to remove the branch.

Three months later, I saw him at the Lagunitas Deli. I asked him "Hey did you ever pull that branch out of the creek?".

He excitedly responded, "No! and its great! There are tiny fish all around it. It's really cool!"

It was music to my ears. Many of us have been conditioned to think of fallen trees as unsightly or even possibly a barrier to fish migration. Nothing could be further from reality. Fish need woody debris to survive and thrive. If we reduce creek complexity by removing woody debris, the number of juveniles that survive will be diminished, and reduce the chance that the magnificent coho and steelhead will return each winter to spawn in the creeks that run through our backyards.

So please, when it comes to Woody Debris, Let it Be.

Reuven Walder

To learn more about the importance of woody debris to salmonids and the stream ecosystem as a whole, contact us.