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Conservation Issues of the Ventana Chapter | santa cruz county

Changing County policy on instream woodwould be good for fish
Big logs in creeks provide critical habitat

January 2009
Healthy Stream
A log has fallen across this creek forming a deep pool on the upstream side where fish can hide. Photo by Kevin Collins

by Kevin Collins

Santa Cruz County is considering modifications to its log jamb removal program. This is very good news for local fish and wildlife. There is a profound misunderstanding by the general public about how in-stream wood creates fish habitat and stabilizes stream banks.

In the past the County cut up logs and large trees that fell into area streams. They believed such wood caused flooding and blocked migrating salmon and steelhead. After many years of research by scientists all over the country, this notion has been thoroughly rejected. Now scientists recommend reintroducing large logs and stumps to denuded streams in an attempt to replace lost habitat for endangered coho, threatened steelhead, threatened red-legged frogs, and other aquatic wildlife.

Such wood is also critical to western pond turtles, salamanders, and other wildlife. Where wood objects are present in streams, juvenile fish take refuge during the summer. Western pond turtles rest on logs in the middle of streams where they are safe from attack by predators.

Trees will fall across and into streams naturally over time. Simply allowing these logs and other in-stream wood to remain would be a huge benefit to our vanishing steelhead and coho salmon populations. Of all the actions we could take to improve fish habitat, this would be by far the easiest, least expensive, and one of the most effective.

Large logs help create deep pools and hiding places where fish can rest and escape predators. During high water flows, when steam flow becomes violent, this wood provides shelter from fast water that otherwise might flush young fish out of the river too soon in their life cycle. Instream wood creates hydraulic vortexes that sort out and deposit spawning gravels at the downstream rim of pools. This high-quality spawning gravel is very scarce in local steams full of sediment.

It was previously thought that clearing streams of wood prevented log jambs. Many readers will remember the floods in January 1982 and in March 1995. The log jams that occurred during those storms were not caused by wood that was already in the stream channels, but rather by trees thrown into streams by landslides and debris slides during the storms, as confirmed by research.

In cases where a log jam forms against a bridge pier or directs water in a way that undermines a road, the County has the emergency authority to protect bridges and roads. If no emergency exists, the County (and private landowners) must consult with Fish and Game and the National Marine Fisheries Service before moving or cutting in-stream wood.

Most of the time instream wood is no threat to property. It can help protect stream banks, and by collecting sand and cobbles, actually slow the down-cutting of stream beds. With our new understanding of the critical function performed by logs in streams, we can temper our fears with a fresh understanding of how instream wood works to improve fish habitat and make our streams healthy and stable.

Please contact the Santa Cruz County Supervisors to tell them you support a new policy on instream wood based on science and not on fear and misunderstanding.

Email addresses of supervisors:



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