Holiday site with parking by river (4)
I believe the answer is:
camp
'holiday site' is the definition.
(camp site)
'parking by river' is the wordplay.
'parking' becomes 'p' (abbreviation on road signs).
'by' means one lot of letters go next to another.
'river' becomes 'cam' (river in Cambridge, England).
'p' put after 'cam' is 'CAMP'.
'with' is the link.
(Other definitions for camp that I've seen before include "Stay in tents" , "Military installation < affected" , "doctrinaire group" , "military depot" , "the military life" .)