How else perhaps swimmers appear (4)
I believe the answer is:
eels
'swimmers appear' is the definition.
I can't judge whether this definition defines the answer.
'how else' is the wordplay.
'how' indicates an anagram (I've seen this in other clues).
'else' anagrammed gives 'EELS'.
'perhaps' is the link.
Can you help me to learn more?
(Other definitions for eels that I've seen before include "Abstract nineteen sixties style" , "Anguillae" , "Long thin fish" , "eg Conger" , "Odd fish found in the lees" .)