Switzerland

Well done CuriousJM! For cmessina I can add that the shape of the glacial top of the Mount Titlis behind is well known to Swiss residents and tourists, as it represent as well the logo of the region: external link and external link

cmessina - Thanks for your comments. Basically I did reverse image search and one of the results mentioned Engelberg. I then started looking for lakes in Engelberg as well as matching scenery in Google Street Views and Google Photos.

@CuriousJM how were you able to find the location that quickly?! That's amazing

Original Flickr image - external link
Unfortunately it doesn't give location.