Come down by river in the country (6)
I believe the answer is:
poland
'country' is the definition.
(Poland is an example)
'come down by river' is the wordplay.
'come down' becomes 'land' (I've seen this before).
'by' says to put letters next to each other.
'river' becomes 'po' (Italian river).
'land' after 'po' is 'POLAND'.
'in the' is the link.
(Other definitions for poland that I've seen before include "Slovakia's northern neighbour" , "Old pan (anag)" , "EU member" , "in E" , "Its capital is Warsaw" .)