Track and follow across river (5)
I believe the answer is:
trail
'track' is the definition.
(I've seen this before)
'follow across river' is the wordplay.
'follow' becomes 'tail' (I've seen this before).
'across' indicates putting letters inside.
'river' becomes 'r'.
'tail' going around 'r' is 'TRAIL'.
'and' is the link.
(Other definitions for trail that I've seen before include "Spoor - lag behind" , "Track, route" , "Forest path" , "Track or mark left by something that has passed" , "Rural footpath" .)