Do very little about river debris (5)

I believe the answer is:

dross

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'debris' is the definition.
(thesaurus)

'do very little about river' is the wordplay.
'very little' becomes 'ss' (I can't justify this - if you can you should give a lot more credence to this answer).
'about' indicates putting letters inside.
'river' becomes 'r' (abbreviation for river).
'do'+'ss'='doss'
'doss' placed around 'r' is 'DROSS'.

Can you help me to learn more?

(Other definitions for dross that I've seen before include "Worthless or dangerous material" , "Worthless matter" , "Impurity" , "Waste coal - rubbish" , "of no value" .)

I've seen this clue in The Times.

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