Part with a message in English river (6)
I believe the answer is:
thames
'english river' is the definition.
(I've seen this before)
'part with a message' is the wordplay.
'part' indicates a hidden word.
'THAMES' can be found hidden inside 'with a message'.
'in' is the link.
(Other definitions for thames that I've seen before include "The Ma's in the river" , "The Isis at Oxford" , "River at Henley" , "Sam the river" , "River at Runnymede" .)