The title says it all...
I assume it requires very slow freezing sheltered from the wind. Undercooled water, maybe?
- A Reddit thread talks about Delaunay triangulation, but that does not explain how it forms.
- Many sites claim it is in Switzerland without further info.
- A comment in another Reddit thread states It happens when there is a significant change in gravitational force during the freezing process.
Also, there was a lot of water vapor hovering just above the surface during a rapid freezing process, but I doubt that gravitational effect.
BTW While researching this I found this beautiful page 18 Beautiful Frozen Lakes, Oceans And Ponds That Resemble Fine Art - several of the pictures there would merit a separate question ;-)
It has a similar picture claiming to be from a frozen pond In Southern Oregon, USA*:
* But a Google image search finds claims of Switzerland, again.