Bad sort in river for ten years (6)
I believe the answer is:
decade
'ten years' is the definition.
(a decade is ten years)
'bad sort in river' is the wordplay.
'bad sort' becomes 'cad' (I am not sure about this - if you are sure you should believe this answer much more).
'in' means one lot of letters goes inside another.
'river' becomes 'Dee' (River Dee).
'cad' placed into 'dee' is 'DECADE'.
'for' is the link.
Can you help me to learn more?
(Other definitions for decade that I've seen before include "Tenth of a century" , "The 1960s, for example" , "Ten year period" , "Time period" , "Ten consecutive years" .)