Reddish insect by river for a drink (6,4)
I believe the answer is:
ginger beer
'a drink' is the definition.
(I know that ginger beer is a type of drink)
'reddish insect by river' is the wordplay.
'reddish' becomes 'ginger'.
'insect' becomes 'bee' (bee is a type of insect).
'by' says to put letters next to each other.
'river' becomes 'r' (abbreviation for river).
'ginger'+'bee'+'r'='GINGER-BEER'
'for' acts as a link.
(Other definitions for ginger beer that I've seen before include "Spicy drink" , "Fizzy drink" , "Non-alcoholic drink" , "Sparkling drink" .)