"and there was a dam that controlled the water level of Sturgeon and therefore Deux Rivers. True?"

don't know about history, but there is no sign of there ever having been a dam on Malign River - that is a huge span to have put a dam in, especially with the current.  Logical place would have been at the first rapid, but I have never seen even the faintest sign that a dam or any other structure had ever been there - usually, you can see some sign of dams or roads, like the dams on Bentpine Creek which had nothing to do with level of Sturgeon lake, but wer used to raise the water level in the creek for transporting logs.  years ago, you could still see the remains of a houseboat in Bentpine, but I didn't notice that last time through there.

logically, there was no reason whatsoever to raise the level of Sturgon Lake - if you wanted to raise the water level in Deux Rivieres, you could much more easily just put a dam in there.