I think the building to the right side of the lake is the "pumping station" for the Raccoon Mountain reservoir. The black line on the left of the reservoir shows the high water line. I don't know that much about producing electricity but I'll try to explain what they do here. Water is pumped up from the Tennessee River to the top of the mountain to fill this reservoir. They pump it up when demand for electricity is low, so it doesn't cost as much. Then when the demand goes up, they release the water through a tunnel down through the generators in the bottom of the mountain and it produces electricity. Click here for more information about this pumped-storage power plant.