Gold found in river, fast-moving stream (7)
I believe the answer is:
torrent
'fast-moving stream' is the definition.
(I've seen this before)
'gold found in river' is the wordplay.
'gold' becomes 'or' ('or' is the heraldic name for gold).
'found in' indicates putting letters inside.
'river' becomes 'trent' (I've seen this before**).
'or' put inside 'trent' is 'TORRENT'.
(Other definitions for torrent that I've seen before include "fast-moving flow" , "Raging flood" , "Rushing stream, flood" , "Inundation" , "Overwhelming flood" .)