Scotland's largest inland body of water by area (4,6)
I believe the answer is:
loch lomond
'scotland's largest inland body' is the definition.
I know nothing about this answer so I cannot judge whether this works.
'water by area' is the wordplay.
'water' becomes 'loch' (a loch is a body of water).
'by area' becomes 'lomond' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'loch'+'lomond'='LOCH LOMOND'
'of' acts as a link.
Can you help me to learn more?
(Another definition for loch lomond that I've seen is " Scottish lake".)