White water (6)
I believe the answer is:
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">white water</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 rapids that I've seen before include "Where rivers run fast" , "Part of a river where the current is very fast" , "what intrepid canoeist enjoys" , "Current hazard" , "Fast-flowing river stretches, white water" .)