Still very warm in river (5)
I believe the answer is:
photo
'still' is the definition.
(I've seen this before)
'very warm in river' is the wordplay.
'very warm' becomes 'hot' (I've seen this before).
'in' means one lot of letters goes inside another.
'river' becomes 'Po' (Italian river).
'hot' going into 'po' is 'PHOTO'.
(Other definitions for photo that I've seen before include "Camera image" , "Snap, pic" , "Snap, picture" , "In brief, a snapshot" , "This race finish is very close" .)