Not wild about hour taken by southern river (6)
I believe the answer is:
thames
'river' is the definition.
(English river)
'not wild about hour taken by southern' is the wordplay.
'not wild' becomes 'tame' ('tame' is the opposite to 'wild').
'about' indicates putting letters inside.
'hour' becomes 'h' (abbreviation).
'taken by' means one lot of letters go next to another.
'southern' becomes 's' (abbreviation).
'tame' going around 'h' is 'thame'.
'thame'+'s'='THAMES'
(Other definitions for thames that I've seen before include "One going to live abroad" , "Capital's river" , "River at Henley" , "London river" , "'Old Father ___'" .)