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Wild guess - Mummelsee?

Hint: no wet suit required

https://photos.smugmug.com/Holidays/Eygpt-Nov-2007-underwater/i-R5jKVNR/0/4c90ab69/XL/CNV00025-XL.jpg

It was back in 2011 and don’t have a detailed itinerary! So I stand to be corrected - this was taken at the same time
...

A little way up Glen Nevis. Not sure if there was a specific name.

Somewhere in Scotland

https://photos.smugmug.com/Watches/n-T3crH/Others/Outside/i-c8p53dZ/0/19f78112/XL/DSC_3990-XL.jpg