Mini– “science lesson”:
Mt Mazama erupted 7,700 years ago- blowing off the top of the mountain and leaving a crater behind.
The former mountain is now a caldera filled with a 2,000 foot deep snow-melt lake… A Crater Lake.
Shorter wave lengths of light (blues) are more easily scattered than absorbed- and the depth of the lake helps to redirect this scattered light back up to the surface… hence the bluest of blue waters- clean and clear too.
This place is seriously beeeeeautiful.