The frozen waterfall
It’s not only power stations that can slow down the rushing water, weather can too. Even the most powerful of waterfalls can be slowed down by freezing cold, and there was a time when the river leading up to the Falls, and the Falls themselves, have frozen.
In 1848, on March 29, Lake Erie which feeds the Falls froze over, and prevented water from reaching them. Sometimes when it’s really cold, sheets of ice appear on top of the water, due to the mist and spray freezing. The water is always moving underneath, though.