Bird plunging into each lake non-stop (7)
I believe the answer is:
eternal
'non-stop' is the definition.
(I've seen this before)
'bird plunging into each lake' is the wordplay.
'bird' becomes 'tern' (tern is a kind of bird).
'plunging into' means one lot of letters goes inside another (I've seen this in other clues).
'each' becomes 'ea' (abbreviation).
'lake' becomes 'L' (geographical abbreviation).
'tern' put into 'ea' is 'eterna'.
'eterna'+'l'='ETERNAL'
(Other definitions for eternal that I've seen before include "Ceaseless" , "non-stop" , "Existing forever" , "with lasting benefit" , "Never-ending, existing always" .)