(Double post.....Be sure to see my nature post below)
This is basically steam released by the power plant after calcium has been added to the coal to remove the sulfur. It results in big piles of calcium sulphate ash like in the picture below. (My husband took me to see this, since he has been doing some engineering work there recently) I know that everyone won't find it beautiful, but it is "home grown" energy rather than foreign oil.
ADDITION: My husband has added this information in the comments: "You didn't mention that the calcium sulfate ash is now being recycled into filler material for such things as concrete and drywall, so other materials don't have to be mined for those purposes."
These stacks are near Mt. Vernon, IN along the Ohio River south of where I live.
.........near Princeton, IN along the Wabash River.
Looks pretty much the same, no matter where you see them!