Large duck that lady doctor put in pool of water (9)
I believe the answer is:
sheldrake
'large duck' is the definition.
(I've seen this before)
'lady doctor put in pool of water' is the wordplay.
'lady' becomes 'she' ('she' refers to a woman).
'doctor' becomes 'dr' (abbreviation).
'put in' is an insertion indicator.
'pool of water' becomes 'lake' (I can't explain this - if you can you should believe this answer much more).
'dr' inserted within 'lake' is 'ldrake'.
'she'+'ldrake'='SHELDRAKE'
'that' acts as a link.
Can you help me to learn more?
(Other definitions for sheldrake that I've seen before include "Large crested diving duck" , "natural swimmer" , "flighty type" , "Diving duck with serrated bill" , "Bird" .)