Large Woody Debris Structures

Large Woody Debris (LWD) structures are the MSG’s most direct salmon habitat enhancement projects.  Logs and boulders are delicately placed in key areas in a stream corridor to provide or improve fish habitat.

How are they built? The LWD structures are constructed in place using an excavator, then anchored together by hand using rebar and thick cables.

How do they work? When water flows against the structure the logs and boulders scour out a hole in the streambed.  This scouring removes excess sediment and creates a pool under the structure.  The structure itself shades and protects the pool from hot sunlight and predators such as birds.  The cold, sheltered water is an ideal habitat for fish and other aquatic life.

Did You Know?

In the past people thought large logs were barriers to fish passage, and they were removed from streams.  Now we know that large wood is essential to a healthy stream ecosystem, so we are working hard to put it back!