Possibly harmful sort of bloom on a little girl (5)

I believe the answer is:

algal

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'possibly harmful sort of bloom' is the definition.
I can't tell whether this definition defines the answer.

'on a little girl' is the wordplay.
'on' means one lot of letters go next to another.
'little' becomes 'l' (abbreviation for little).
'girl' becomes 'gal' (synonyms).
'a' put next to 'l' is 'al'.
'al'+'gal'='ALGAL'

Can you help me to learn more?

(Other definitions for algal that I've seen before include "Pertaining to such as seaweeds" , "Relating to seaweeds, etc" .)

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

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