Paul, I haven't had a chance to fish Pend Oreille yet but I have fished Kootenay Lake in B.C. It also has the same big bruiser strain of Rainbow in it. I have seen a picture of a 75 pound fish taken from Jewel Lake at the turn of the Century. Amazing fish.
On Kootenay, most people fish the way you describe. During the Fall, Winter and Spring, the fish are on the surface and they troll a big polar bear hair bucktail fly on planer boards. During the Summer, the fish hold in the thermal layer so they are using downriggers. I spoke to a fly shop owner in Kelso, B.C. and she said that she fished big, light colored streamers that imitated the silvers in the lake. Her biggest to date was about 8 pounds (what the local guides would disgustingly call a shaker as they throw it back) but she had other fly fisherman tell of better success using this method. I would stop by Fins and Feathers in Cour D Alene next time you are in the area. The guys seem to know their stuff and will set you on the right path. Mike
