Fly_Guy,
According to the regulations, "ALL FRESHWATER AREAS are CLOSED to fishing for SALMON, Dolly Varden/bull trout and GRASS CARP unless listed as open in Special Rules"(p. 20).

The North and South Forks of the Stillaguamish are closed to fishing for salmon at all times. The main river, below the confluence of the North and South Forks, is (or was last year) open to fishing for salmon from Septmber 1st to December 31st
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PS