Bird in river joining lake (5)
I believe the answer is:
ousel
'bird' is the definition.
(ousel is a kind of bird)
'river joining lake' is the wordplay.
'river' becomes 'ouse' (Yorkshire river).
'joining' says to put letters next to each other.
'lake' becomes 'L' (geographical abbreviation).
'ouse'+'l'='OUSEL'
'in' acts as a link.
(Other definitions for ousel that I've seen before include "Othello?" , "Bird; louse (anag.)" , "it goes flying" , "Thrush from Seoul, strangely" , "Type of thrush" .)