Man-made waterway (5)
I believe the answer is:
canal
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">man-made waterway</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for canal that I've seen before include "eg Grand Union" , "navigate this?" , "Man-made watercourse" , "Aqueduct" , "Artificial waterway for barges" .)