Powerful circular current (6)
I believe the answer is:
vortex
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">powerful circular current</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 vortex that I've seen before include "Powerful circular current of water" , "Whirlpool current" , "Whirling fluid" , "Whirling motion" , "Engulfing swirl of e.g. whirlpool" .)