Point of no return; stream in northern Italy (7)
I believe the answer is:
rubicon
This clue is a double definition.
'point of no return' is the first definition.
(as in the phrase 'crossing the Rubicon')
'stream in northern italy' is the second definition.
(I've seen this before)
(Other definitions for rubicon that I've seen before include "Stream in north Italy that Julius Caesar crossed in 49 BC" , "River, its crossing decisive" , "Caesar crossed this river to take irrevocable step" , "Point of no return (which Caesar crossed in 49BC)" , "Cross it to pass the point of no return" .)