I got curious about Niagara Falls and looked at the aerial view on Google Maps. I noticed a dam named International Control Dam a little ways upriver from the falls. This dam only goes halfway across the Niagara River, between an unnamed island and the Canadian side. There’s no dam on the other side of that island. What’s the point of having a dam going only halfway across a river?
The dam has adjustable gates, and is used to slow the rate of flow over the Falls, allowing more water to be drawn into intake pipes, a little further upstream on the river, that deliver water to the two massive reservoirs and power plants in the gorge. It also can also control how much water flows over the Canadian falls, versus the American falls. The International Control Dam is jointly operated by New York State Power Authority and Ontario Hydro.
Apparently it’s enough for the purpose.