When did Victoria falls become a wonder?

One could say that Victoria Falls has always been a wonder - since humankind first laid eyes on it.
The complication in this question is that there is no official list of wonders. Instead, there are many lists, compiled by many sources along many different themes, of which Victoria Falls is included in some, but not others.
We should appreciate Victoria Falls for the natural wonder that it is - the widest continuously falling sheet of water in the world.