Nightbird in Channel Islands extremely lucky having aquatic plant (3,4)

'aquatic plant' is the definition.
(cow lily is a kind of aquatic plant)

'nightbird in channel islands extremely lucky' is the wordplay.
'nightbird' becomes 'owl' (I've seen this before).
'in' means one lot of letters goes inside another.
'channel islands' becomes 'ci'.
'extremely' says to hollow out the word (remove centre letters).
'lucky' with its middle taken out is 'ly'.
'owl' going into 'ci' is 'cowli'.
'cowli'+'ly'='COW LILY'

'having' acts as a link.