Parasites and disease would be worse case scenario if getting wood from a lake. If the pieces are sized enough to be boiled then I would boil it. But yea bleaching it works as well. Never tried getting wood from a lake to use but everywhere I read they always say to bleach or boil.
I always use pieces from the wild that are already water logged. That way I know there is little chance of it releasing any tannins into the tank. To clean it, I just hit it with the high pressure hose and then give it a good wash/soak with diluted pool chlorine to kill any nasties. Pool chlorine is easily neutralized with prime before introducing the timber to the tank.