Waterbird heads for good river estuary to live (5)
I believe the answer is:
grebe
'waterbird' is the definition.
(type of waterbird)
'heads for good river estuary to live' is the wordplay.
'heads for' indicates taking the first letters.
'to live' becomes 'be' ('be' can be a synonym of 'live').
The initial letters of 'good river estuary' is 'gre'.
'gre'+'be'='GREBE'
(Other definitions for grebe that I've seen before include "Freshwater diving bird" , "Crested water-bird" , "Aquatic bird that builds floating nests" , "Swimmer" , "I'll dive in" .)