After the Great Flood on Shenango, a few years back, not sure how long ago. If you know where Big Bend is, on the pillars for the bridge, you can still see how high the water was. Any ways, the Corp couldn't figure out at first, thy the water just kept rising. So they contacted Pymatuning Lake, and asked them if they were dumping water, which they were. So then the Corp took control of when and how much they can dump. Pymy vcan only dump now, after getting approval form the Corp. That is why I asked about Wilhelm. What stream, does it dump into? They may be controlled, by the Corp also.
Will add that with the water so high, and then the temps dropped, trees were getting frozen, and then bursting apart.
Okay, I looked at a map of Mercer County, and Lake Wilhelm, doesn't drain into the Shenango River system, or at least, not till after the dam.