Canadians too, I believe. So North Americans. I’m not sure how it started, but it’s pervasive.
The funny thing is that when Americans use the word “watershed” metaphorically, they stick with the original meaning, a divide.
I’m American, and grew up using the word in the way of our people. It was a minor shock to me to learn that people from other English-speaking countries used the word to mean the opposite of what I meant. It was an enormous shock to realize that the way I used the word as a metaphor showed that the foreigners had it right. You could say it was a watershed moment.
