If you rely on the horn even at the dam you're foolish. 10 fold at night!. You should watch the water level yourself. I've camped at McC's dozens if not over a hundred times. Unless the wind is perfect you won't hear it. Even then, relying on that is asking for trouble. They'll find you feet up down around Calico Rock. Another thing. If the fishing turns on like crazy you better watch out. That's what happens right before the flow increases. I think the trout hear the water coming or something.