Float around a river - that's sweet (7)
I believe the answer is:
caramel
'that's sweet' is the definition.
(caramel is a kind of sweet)
'float around a river' is the wordplay.
'float' becomes 'camel' (camel can mean a float for lifting a sunken vessel).
'around' means one lot of letters goes inside another.
'river' becomes 'r' (abbreviation for river).
'a'+'r'='ar'
'camel' going around 'ar' is 'CARAMEL'.
(Other definitions for caramel that I've seen before include "Sugar solution heated till brown" , "Dark brown substance" , "Burnt sugar used for flavouring" , "Chewy sweet - burnt sugar" , "It's produced by heating sugar until brown" .)