Fish Issues

Background

Both Chinook salmon and steelhead have been identified in Lower Walnut Creek.  Currently, these anadromous fish cannot swim upstream beyond Drop Structure #1 except during very high flows.  This structure serves an important role in keeping the channel stable during large storm events, but its 13-foot vertical weir is not passable by fish.

Lower Walnut Creek suffers from poor riverine habitat.  Despite this, there were anecdotal reports of spawning Chinook salmon in the creek.  Could this be the case?  To definitively determine the likelihood of fry emergence, the District and the Corps of Engineers commissioned a detailed study of channel conditions, spawning escapement and fry emergence.  The study, lasting from 2004 through 2007, is available on the Reports and Documents page.  

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More information about Chinook salmon via NOAA

Conclusions

The study confirmed the presence of redds in the bed of Lower Walnut Creek, but found very low survival of eggs and fry.  This was attributable to:

  • High percentage of "fines" (fine sediment) that covered up and clogged spawning gravels and
  • Scour that may have washed away eggs and alevins. 

Please see the full study on the Reports and Documents page for more details.