A swan in San Francisco Bay (3)

I believe the answer is:

cob

'a swan' is the definition.
(cob is a kind of swan)

'in san francisco bay' is the wordplay.
'in' indicates the answer is hidden within the clue.
'COB' is hidden within 'san francisco bay'.

(Other definitions for cob that I've seen before include "mount" , "Hazelnut" , "Round loaf of bread" , "mixture of clay and straw" , "Horse, male swan and loaf of bread" .)

I've seen this clue in the Evening Standard.

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