I have fished the Snake from the mouth to 95 miles above Lewiston for steelhead. Hell's Canyon is an awesome place. A lot of cool history. A good way to see it and sometimes fish a little is to book a trip with the mail boat. It is usually a two day trip once a week when they deliver the mail from Lewiston up river. I sold my jet boat in 1999, so it has been a few years since I have been up there, but Beamer's used to have the contract to deliver the mail and they went up to Sheep Creek...95 miles up stream. I did not make the mail run per se...I followed a guide I knew to learn a little about the river. It has a few nasty spots.
Behind the dams, we just trolled plugs for steelhead. In the faster current, we 'back trolled' plugs or plugs and shrimp. I am not up to date on the regs, but there was a catch and release fishery for sturgeon up the canyon and we caught some nice bass up there also. The guides have names for the big fish..some of 'em are 8 to 10 feet long and they catch the same ones over and over.