Show a river with fish (5)
I believe the answer is:
array
'show' is the definition.
(I've seen this before)
'a river with fish' is the wordplay.
'river' becomes 'r'.
'with' is a charade indicator (letters next to each other).
'fish' becomes 'ray' (ray is a kind of fish).
'a'+'r'+'ray'='ARRAY'
(Other definitions for array that I've seen before include "Order - arrangement" , "Fine assortment" , "Lay out, arrange" , "Ordered arrangement (of troops)" , "Significant arrangement" .)