Let's just file this one under Crazy Crap You Probably Didn't Know About. At least I know I didn't.
Niagara Falls on the American side were basically shut off for several months in 1969 as US Engineers diverted flow to the Canadian side to...apparently repair some fault lines below the falls.
Apparently several rock slides caused some predictions that after 12,000 years of flowing predictably and torrentially, Niagara Falls, due to crumbling fault lines, would at some point in the not too distant future would stop flowing....? So the Army Corps of Engineers removed some rubble, and bolted some fault lines, and started the water flowing again.
Anyway. Pretty interesting. These pictures were found in a shoebox buried in somebody's grandfather's house.