Animal in a lake - boar, possibly (5,4)
I believe the answer is:
koala bear
'animal' is the definition.
(I've seen this before)
'a lake boar possibly' is the wordplay.
'possibly' is an anagram indicator.
'a'+'lake'+'boar'='alakeboar'
'alakeboar' with letters rearranged gives 'KOALA BEAR'.
'in' acts as a link.
(Other definitions for koala bear that I've seen before include "Eucalyptus eater" , "Creature" , "Australian resident" , "Aussie tree-hugger" , "Australian animal" .)