Sure sounds like Algonquin dam. Except the part with a moving gate is maybe an eighth of the river (nowhere near half).A friend was telling me they were working on the dam in Algonquin. He said the state ran out of money and stopped working. Half is ok the other half is left open, with no way of closing it. I cannot verify this as true, all I can say is I hope not. It will run fishing, boating, etc for all concerned.