Hey, gotta get the terminology right; South Fork, North Fork. The South Fork doesn't have the easy accessibility of the North Fork and the inhabitants of Canyon Creek are of the Deliverance ilk (scary). The North Fork is accessible from the road at the Lime Quarry, Cicero,Oso, Whitman Bridge, the Mermaid, Seapost, Hazel, Boulder River, Fortson Mill and Fortson Hole and after the river comes down from spring runoff you can cover long stretches of it wading. The North Fork is open year round and is restricted to fly fishing from April 16 to November 30 and is catch and release for wild fish (intact adipose fin) from March 1 to November 30. The native fish spawn in Deer Creek (closed to fishing) and are usually in the river below Oso by July. The Skamania-strain fish that have been stocked above Oso may be in the river as early as late April or May along with late winter-run fish. Many patterns are popular and effective. In the early season, when the water is high and off-color, many of the old standards; Skykomish Sunrise, Purple Peril, Brad's Brat, Green-Butt Skunk, Polar Shrimp, or any of the Marabou Spiders work fine. As the water drops, warms and clears try some dries like Haig-Brown's Steelhead Bee, Lemire's Greaseliner or any of a number of October Caddis patterns.
