The answer is very simple. Ask any worker of the Corps of Engineers and they will give you the same answer:

These are flood control lakes. Their purpose is to control flooding. Things like fishing, boating, camping, cabins and lakefront property are simply seconday benefits. None of them will ever interfere with the flood control purpose of the lake.

Someone, somewhere in the COE has determined that Barren needs to hold back water right now for flood control purposes.