Legendary ship making a river journey (4)
I believe the answer is:
argo
'legendary ship' is the definition.
(I've seen this before)
'a river journey' is the wordplay.
'river' becomes 'r' (abbreviation for river).
'journey' becomes 'go' (I've seen this in other clues).
'a'+'r'+'go'='ARGO'
'making' is the link.
(Other definitions for argo that I've seen before include "Ship used by Jason in his search for the Golden Fleece" , "Jason's legendary ship" , "Old craft" , "Ship Jason sailed to find the Golden Fleece" , "Famous ship" .)