Shad are a blast on light tackle. You can fish from shore below the dam, from mainland or the island toward Oregon side, though it is all very rocky/snaggy so take lots of terminal tackle.
Locally, those fish seem to prefer small shad darts, chartreuse with gold hooks but no hair or feathers for a tail. (Visit the general store in Stevenson if you can't find these near home.) Shouldn't need much weight to get to them. They'll take flies too, in a variety of colors but usually with a shiney component of gold or silver.