On German lake, last of the morning sun shimmers (6)
I believe the answer is:
gleams
'shimmers' is the definition.
(both can mean to shine)
'on german lake last of the morning sun' is the wordplay.
'on' is a charade indicator (letters next to each other).
'german lake' becomes 'gl' (this might be a standard abbreviation of which I'm unaware).
'last of' suggests the final letters.
'morning' becomes 'am'.
'sun' becomes 'S' (abbreviation).
The final letter of 'the' is 'e'.
'gl' put next to 'e' is 'gle'.
'gle'+'am'+'s'='GLEAMS'
(Other definitions for gleams that I've seen before include "Brief showings of soft light" , "Shines brightly" .)