Herdsman finding river in port (6)
I believe the answer is:
drover
'herdsman' is the definition.
(synonyms)
'river in port' is the wordplay.
'river' becomes 'r' (abbreviation for river).
'in' means one lot of letters goes inside another.
'port' becomes 'dover' (port town in Kent).
'r' put into 'dover' is 'DROVER'.
'finding' is the link.
(Other definitions for drover that I've seen before include "Person moving sheep or cattle from one place to another" , "Hugh the --, opera by Vaughan Williams" , "One driving cattle" , "I bring along many animals" , "Man who herds cattle" .)