Try to find any change in bottom contour, even only a couple of feet. Look for any cover in the water, fallen trees, remaining weeds, etc. If there are rocks look for these. Otherwise drill, drill, drill. I fish a lake like this in Ohio and sometimes you just drill 100 holes and move until you find them, I usually look deeper first and work shallower. Hopefully you have a gas auger, otherwise this approach is not real practical.
