Harsh sounds made by river snakes (5)
I believe the answer is:
rasps
'harsh sounds' is the definition.
(I've seen this in another clue)
'by river snakes' is the wordplay.
'by' means one lot of letters go next to another.
'river' becomes 'r' (abbreviation for river).
'snakes' becomes 'asps' (asp is a kind of snake).
'r'+'asps' is 'RASPS'.
'made' is the link.
(Other definitions for rasps that I've seen before include "Jars" , "Scrapes" , "speaks hoarsely" , "fruit briefly" , "Grates harshly" .)