Don't fish the Columbia much myself, but do have some friends that fish it a lot. They mostly troll plugs just above McNary dam in the slack water pool. Troll slowly, just fast enough to work plugs. They try to target water from 10 to 20 ft deep. Seems as if fish that just come through the dam don't always hug the bottom. Again, troll slowly.
Also, I have caught several steelies below the dam using walleye gear (in line spinner blades with crawlers) bouncing the bottom. These were caught off mouth of the Umatilla R. or on the Wa. side just upstream of the bridge. Good luck. By the way, my sources say the fishing should pick up as water starts to cool in a month or so.