That sounds pretty expensive, never mind environmentally risky, and I don't think it would even work. First, that habitat doesn't appear to be particularly productive; the trout populations are fair to middling at best. Second, no anadromous fish have ever had access to those habitats; they're not necessarily suitable or productive habitats for steelhead.
But I kind of like the sentiment, and I have a more modest proposal. Removing the manmade fish-passage barrier WDFW maintains at the Tokul Creek Hatchery would re-open about 50 miles of good summer steelhead spawning and rearing habitat in the lower Snoqualmie Basin. In 1996 the state recognized the WDFW diversion dam on Tokul Creek as the most significant manmade fish-blockage in the entire Snoqualmie watershed. In 2004, it's still blocking fish (though WDFW, through WT initiative, does trap and transport ESA-listed chinook around the barrier in the fall).
WDFW acknowledges that there are at least 38 fish-passage barriers associated with their various hatcheries. Taken together, they probably add up to the tens or hundreds of miles of habitat you're talking about, perfectly good habitat that steelhead and salmon used for thousands of years, that they could use again if the barriers were removed or fixed.
Hatchery barriers aren't the only problem. of course. Simple road culverts and small water diversions often block fish from utilizing dozens of miles of otherwise productive habitat. Washington Trout works with public agencies, community organizations, and individual property owners to evaluate, identify, prioritize, and remove fish-passage barriers throughout the state.
Look for more information about the WT "Habitat Lost and Found Program" at
http://www.washingtontrout.org .
Ramon Vanden Brulle
Washington Trout