Cairo waterway (4)
I believe the answer is:
nile
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">cairo waterway</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for nile that I've seen before include "Green" , "Egypt's river" , "River (which is originally blue and white)" , "Line (anag)" , "River that's Blue and White" .)