In Patagonia Argentina, where I fish, there's a big nice mayfly, a Hexagenia genus, which produces hatches during Spring and Summer. (September to March)

They live mostly in big glacial euthropic lakes like the Nahuel Huapi, Traful, etc. Without a doubt it is a relative to the Hexagenia Limbata, which is very well known in US.

I saw it many times hatching during calm sunny mornings while I was fishing the lakes. It's a bug that can be imitated on regular dry fly hooks between #8-10. Its color is pale-orange or similar to a wheat seed.