Morning dipping in the Southern river (6)
I believe the answer is:
thames
'river' is the definition.
(English river)
'morning dipping in the southern' is the wordplay.
'morning' becomes 'am' (as in th:00 AM).
'dipping' becomes 'the' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'in' indicates putting letters inside.
'the southern' becomes 's' (abbreviation).
'am' going inside 'the' is 'thame'.
'thame'+'s'='THAMES'
Can you help me to learn more?
(Other definitions for thames that I've seen before include "London flood control" , "The Ma's in the river" , "The Isis at Oxford" , "Longest English river" , "Sam the river" .)