GW,
My pond has been full for 6 months.
The Sweet Gum is right on the water line. That particular part of my pond landscape was occasionally "marshy" before I flooded it so perhaps it had alrready aclimated to the wet soil? Its a really large tree.
To another point on oaks above. I lost a nice red oak that I considered totally out of the water line. Go Figure.
I also have a couple of water oaks hanging in there with at least some of their root system in the water line.