Get to part of river (5)
I believe the answer is:
reach
I believe this is a triple definition!
'get to' is the first definition.
(synonyms)
'part' is the second definition.
(reach is a kind of part)
'of' is a link.
'river' is the third definition.
(I know that reach is a type of river)
(Other definitions for reach that I've seen before include "Put out the hand for a part of the river" , "Scope; get to" , "stretch of canal between locks" , "Get in touch" , "Attain; extend to" .)