Use the Cowlitz below Mayfield Dam gage, it will give you the most acurate reading for Blue Creek. Ideal flows for the Cowlitz this time of year is between 6000 CFS and 9000 CFS, it is at and has been at 5000 - 5200 CFS for about two weeks now. That gage is only six miles upstream from Blue Creek. The Castle Rock gage is about 15 - 20 miles downstream from where you are fishing. Hope this helps ya out.
Good luck and tight lines, Jeff

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