Change course holding river route (5)
I believe the answer is:
track
'route' is the definition.
(track is a kind of route)
'change course holding river' is the wordplay.
'change course' becomes 'tack' (I've seen this before).
'holding' indicates putting letters inside.
'river' becomes 'r'.
'tack' going around 'r' is 'TRACK'.
(Other definitions for track that I've seen before include "Shadow" , "Course over which races are run" , "Single item on a CD" , "one of a number on record" , "Foorprint or trail" .)