Immerse at lower level around river (5)

I believe the answer is:

drown

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'immerse' is the definition.
(thesaurus)

'lower level around river' is the wordplay.
'lower level' becomes 'down' (I can't explain this - if you can you should give a lot more credence to this answer).
'around' means one lot of letters goes inside another.
'river' becomes 'r' (abbreviation for river).
'down' going around 'r' is 'DROWN'.

'at' is the link.

Can you help me to learn more?

(Other definitions for drown that I've seen before include "Go under" , "Perish in water" , "Flood; kill" , "Sink" , "Completely conceal" .)

I've seen this clue in The Sun.

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