CW,
Exactly what DIED said in general.
In particular, I have seen many water oaks (quercus nigra)with their roots half in and half out of the water that grow just fine. If the roots on the dry bank are partially exposed, you can usually cover them with an inch or 2 of light soil with no ill effects. Deep soil or heavy clay will slowly starve them for oxygen. I have 3-4 water oaks on my land right now that have their roots partially or totally submerged for nearly half the year. I don't think the various red oaks would survive that, but the water, scrub, and live oaks seem to tolerate it quite well.
