Landowner has to ring back about river (5)
I believe the answer is:
laird
'landowner' is the definition.
(Scottish term for a landowner)
'to ring back about river' is the wordplay.
'to ring' becomes 'dial' (I've seen this before**).
'back' says the letters should be written in reverse.
'about' means one lot of letters goes inside another.
'river' becomes 'r'.
'dial' reversed gives 'laid'.
'laid' enclosing 'r' is 'LAIRD'.
'has' is the link.
(Other definitions for laird that I've seen before include "Proprietor" , "Estate landowner" , "Scottish owner of large estate" , "Scots landowner" , "Scottish estate-owner" .)