Blend lake used by one artist (6)
I believe the answer is:
fuseli
'artist' is the definition.
(Swiss painter Henry Fuseli, 1741-1825)
'blend lake used by one' is the wordplay.
'blend' becomes 'fuse' (synonyms).
'lake' becomes 'L' (geographical abbreviation).
'used by' is a charade indicator (letters next to each other).
'one' becomes 'i' (Roman numeral).
'fuse'+'l'+'i'='FUSELI'
(Other definitions for fuseli that I've seen before include "'Nightmare' artist (1782)" , "Anglo-Swiss painter" .)