Steven...thanks. And I don't know, I mean I am m not in Patagonia at this time (trout region) but near Buenos Aires. So I'm not fishing; the mayfly appeared at home. I also checked March Browns in this area. Bigger and darker than this relatively pale mayfly. Yes, it's beginning of fall.
However, I think it is very interesting to compare the bugs (in this case a mayfly) that you have in the North America with our insects and see (if any) the differences.
This one is very usual in Patagonian lakesMayfly Traful.jpg.