Weather feature that is on river edge (8)
I believe the answer is:
frontier
'edge' is the definition.
(frontier is a kind of edge)
'weather feature that is on river' is the wordplay.
'weather feature' becomes 'front' (I've seen this in other clues).
'that is' becomes 'ie' ('i.e.' can be a synonym of 'that is').
'on' is a charade indicator (letters next to each other).
'river' becomes 'r'.
'front'+'ie'+'r'='FRONTIER'
(Other definitions for frontier that I've seen before include "Border (not yet crossed?)" , "Outer edge of a settled territory" , "Verge" , "Land-border of a country" , "Wilderness at the edge of settled territory" .)