Why don't the trees in the lake fall over or rot?

In Kansas, in order to have a lake, you have to damn a river up and flood a valley (yes, we have valleys in this part of Kansas!) That means flooding trees and even houses and stuff. And even a bulldozer is at the bottom of our lake somewhere. Here is is, 60 years later, and the trees around the shallower edges are still standing. They’re dead, obviously, but why haven’t their bases long since rotted away and toppled them into the water?