One long in the water? Leave rock (6,3)
I believe the answer is:
conger eel
'one long in the water?' is the definition.
I can't judge whether this defines the answer.
'leave rock' is the wordplay.
'leave' becomes 'conge' (I've seen this in other clues).
'rock' becomes 'reel' (reel can mean to rock around).
'conge'+'reel'='CONGER-EEL'
Can you help me to learn more?
(Other definitions for conger eel that I've seen before include "Predatory sea creature" , "Large slippery fish" , "swimmer" , "Predatory fish" , "long haul?" .)