Be on river and notice skin blemish (5,4)

I believe the answer is:

liver spot

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'skin blemish' is the definition.
The answer and definition can be both body parts as well as being singular nouns.
Maybe there's an association between them I don't understand?

'be on river and notice' is the wordplay.
'be' becomes 'live' (living is a kind of being**).
'on' is a charade indicator (letters next to each other).
'river' becomes 'r'.
'and' means one lot of letters go next to another.
'notice' becomes 'spot' (I've seen this before).
'live'+'r'+'spot'='LIVER SPOT'

Can you help me to learn more?

I've seen this clue in The Times.

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