Henley event (7)
I believe the answer is:
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">henley event</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 regatta that I've seen before include "Number of yachts in sporting event" , "Display of boats" , "which may involve eights" , "Series of yacht races" , "Event for craft" .)