I used to fish for them allot back east. Small clousers in drab colors, baitfish imitations, small poppers, skaters etc. They take dry flies well, and nymphs too.Muddlers and small weighted sculpins worked very well, especially olive and gray or natural rabbit colors.You can use all your trout patterns with success.They like to chase stuff down and kill it. But if they have been educated, caught allot on flies, then you have your work cut out for you.
IN my COlumbia basin bassin days, a small deer hair mouse, say size 6or 4, worked wonders on the Yakima, yes above the dam can be fun! ALso a wobbling foam fly I make, take some yellow foam sheet, and just think flatfish and get creative. For sheer numbers, nothign would beat a dark wolly bugger, dead drifted thru likely looking spots. Stripping it in was really NOT the ticket. Where are you fishing???
For a real challange, go a mile below the dam and work upriver to the carp feeding all along here. These are the pickiest, spookiest most stubborn carp I have ever encountered. Then, just to make it interesting, try it with your wife's Yorkie tucked under you arm cause you promised her you would watch the dog while she went shopping with your sister......
The following suggestions are not from personal experience but are from two different articles on smallmouth fishing on the John Day and Columbia rivers.
These two articles appeared in Northwest Fly Fishing magazine. The John Day article is from Fall 2002 and the Columbia article is from Summer 2000. Both articles are well worth reading reading. Back issues of Northwest Fly Fishing can be ordered from thier web site. http://www.nnwflyfishing.net You may have to call them to order. Contact info is on the site.
Dries: Foam beetles (yellow, red or blue),cork poppers (yellow, white or green, some with rubber legs),Blue Damsels, Chernobyl Ants, Girdle bugs in white, orange, charttreuse, black, yellow, or brown with rubber legs in green, orange,or white.
Wets: Woolly Buggers (black purple, rusty brown, sizes 2 to 6 with and without barbell-weighted eyes), Bitch Creek Specials, Woolly Worms, leech and crayfish patterns, Clouser Minnows in brown/yellow, white/yellow, and white/grey, sizes 1/0 to 4, rabbit-strip Hareworms in sizes 4 to 6 tied on keel hooks(mister twister hook keeper and and Bass worm-style hooks. Sculpins, and smaller nymphs.
I've actually done pretty good when I was using nymphs for smallmouth. For some reason, size 14-18 bh seemed to work well. Also, I have caught them on large scuds, and all the other "standard" smallie flies.