Vessel going round lake casts off (7)

I believe the answer is:

sloughs

'casts off' is the definition.
(sloughing is a kind of casting off)

'vessel going round lake' is the wordplay.
'vessel' becomes 'ss'.
'going round' indicates putting letters inside.
'lake' becomes 'lough' (lough is a kind of lake**).
'ss' going around 'lough' is 'SLOUGHS'.

I've seen this clue in The Telegraph.

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