A tidbit from Randall Munroe’s exploration of what might happen if you tried to funnel Niagara Falls through a straw:
Since people get mad if you turn off the world’s most famous waterfall, they’re required to leave at least 100,000 of those cubic feet per second flowing over the falls for everyone to look at. (50,000 at night or during the off-season). Sometime in the next few years, the falls may be turned off for maintanence.
This level of control is startling.