Ditch or river full of fish? Quite the contrary (6)
I believe the answer is:
trench
'ditch' is the definition.
(I know that ditch can be written as trench)
'river full of fish? quite the contrary' is the wordplay.
I cannot really see how this works, but
'river' could be 'r' (abbreviation for river) and 'r' is found within the answer.
'fish?' could be 'tench' (tench is a kind of fish) and 'tench' is found within the leftover letters.
This accounts for all the letters.
This explanation may well be incorrect...
'or' acts as a link.
Can you help me to learn more?
(Other definitions for trench that I've seen before include "A military ditch for soldiers" , "Ditch dug as fortification" , "Protective ditch" , "Ditch, as a fortification say" , "A ditch dug by soldiers" .)