this waterfall is called "grindwäschi", which means "head wash" in swiss german. It's the borderline between Zug and Walchwil.
The legend about this waterfall says: The people of Walchwil came annually to the fair (Chilbi) of Zug, and when returning to Walchwil they washed their bloody heads under this waterfall. Why they heads were bloody you ask? Alcohol + flirting with other guys girlfriends.
I like this little anecdote. :)