Aquatic legend - she controls men's swimming (4,4,7)
I believe the answer is:
loch ness monster
'aquatic legend' is the definition.
I don't know anything about this answer so I can't tell whether this works.
'she controls men's swimming' is the wordplay.
'swimming' indicates an anagram (letters swim around into a new order).
'she'+'controls'+'mens'='shecontrolsmens'
'shecontrolsmens' is an anagram of 'LOCH NESS MONSTER'.
Can you help me to learn more?
(Other definitions for loch ness monster that I've seen before include "lt's never been found" , "Scots apparition" , "Caledonian enigma" , "Fabulous creature" , "Legendary Scottish apparition" .)