Khartoum's river (4)
I believe the answer is:
'khartoum's river' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for nile that I've seen before include "River associated with Cleopatra" , "long-distance runner in Africa" , "River that's Blue and White" , "River of eastern Africa" , "River (which is originally blue and white)" .)