Bathing beauties tangled in reeds (7)
I believe the answer is:
nereids
'bathing beauties' is the definition.
(creatures of Greek myth)
'tangled in reeds' is the wordplay.
'tangled' indicates an anagram.
'in'+'reeds'='inreeds'
'inreeds' anagrammed gives 'NEREIDS'.
(Other definitions for nereids that I've seen before include "Group of nymphs" , "Mythological sea nymphs" , "Need, sir, could produce seanymphs" .)