French river running north through French station (7)
I believe the answer is:
garonne
'french river' is the definition.
(I've seen this in another clue)
'running north through french station' is the wordplay.
'running' becomes 'on' (eg when a machine is running it is on).
'north' becomes 'N' (synonyms).
'through' means one lot of letters goes inside another (inserted letters go through the word).
'french station' becomes 'gare' (I've seen this in another clue).
'on'+'n'='onn'
'onn' going into 'gare' is 'GARONNE'.
(Other definitions for garonne that I've seen before include "River of Toulouse and Bordeaux" , "French river" , "Toulouse's river" .)