Swimmer skirts river channel? (6)
I believe the answer is:
trench
'channel?' is the definition.
(I've seen this in another clue)
'swimmer skirts river' is the wordplay.
I cannot quite see how this works, but
'river' could be 'r' (abbreviation) and 'r' is located in the answer.
'swimmer' could be 'tench' (tench is a kind of fish) and 'tench' is present in the leftover letters.
No letters remain.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for trench that I've seen before include "at the front" , "A deep ditch, as dug for troops" , "Drain" , "A ditch dug by soldiers" , "Long narrow ditch" .)