From what I understand the power plant is shut down and underwater, therefore not releasing any water from the bottom of the dam.
Some of the power poles are cut, too.
My guess regarding the plant is that there may be a ton of debris blocking the intake screens, preventing water from flowing through the generators. I don’t know how much flow would go through at full electrical output, but I’m sure that it would be enormously helpful in reducing the lake level. And unlike the spillway, that water path is intact.