Save Hebridean island lake that's remarkable (11)
I believe the answer is:
exceptional
'remarkable' is the definition.
(thesaurus)
'save hebridean island lake' is the wordplay.
'save' becomes 'except' (I've seen this before).
'hebridean island' becomes 'iona' (I've seen this before).
'lake' becomes 'l'.
'except'+'iona'+'l'='EXCEPTIONAL'
'that's' is the link.
(Other definitions for exceptional that I've seen before include "Very unusual" , "Outstanding; not typical" , "Out of the ordinary" , "Extraordinary!" , "Unusually good" .)