I grew up close to Niagara Falls and my dad was a firefighter there for ~30 years who had to practice rappelling down the gorge to save people (which sadly happens too frequently).
His favorite story from the last time they "shut the falls off" was that they found tons of loose change in the rocks around the rapids - people were racing to get it and bringing back buckets of money. (Of course, they also found a few bodies as well...)