If I understand correctly, the water level has equalized on both sides of the breach. With no appreciable current flowing through it anymore, it should just be a matter of dumping material into it to close it off, then pumping out the water on the side that's supposed to be dry. I think the strong flow through the breach was the problem up to this point.
I did hear that until they close the breach they can't even begin pumping, so questions about pumps are moot? Is there any danger of the Miss. River (which I've read is higher than the lake) overflowing because of the increased volume?