Niagara Falls Can Be Turned Off?
In the winter of 1969, the Army Corps of Engineers needed to conduct a geological survey of the rock face of the falls and clean up the area a bit. They were going to assess if it was worth cleaning up the rocks and rubble on the American side. So they did what anyone would do. The shut the falls off.
How did they accomplish this? They built a series of coffer dams to reduce the flow of water to the tiniest trickle. Coffer dams are made of welded steel and are usually used in the construction and repairs of bridges and oil rigs.
Bonus fact: It’s not the only time Niagara falls was dry. In 1848, an ice jam up the river caused the Niagara to stay bone dry for nearly 48 hours. Some people took it as a sign the world was ending and attended special services at local churches.