Which swimmer is flushing badly? (8)

I believe the answer is:

lungfish

I'm a little stuck... Click here to teach me more about this clue!

'which swimmer' is the definition.
I can't tell whether this definition defines the answer.

'flushing badly?' is the wordplay.
'badly?' indicates an anagram (I've seen 'badly' mean this).
'flushing' is an anagram of 'LUNGFISH'.

'is' is the link.

Can you help me to learn more?

(Another definition for lungfish that I've seen is " denizens of the river".)

I've seen this clue in the Sydney Morning Herald.

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