Talk a lot about a quiet part of the river (6)
I believe the answer is:
preach
'talk' is the definition.
(I know that preach is a kind of talk)
'a lot about a quiet part of the river' is the wordplay.
'lot' becomes 'c'.
'about' is an insertion indicator.
'a quiet' becomes 'p' (music symbol for 'piano', ie soft or quiet).
'part of the river' becomes 'reh' (I am not sure about this - if you are sure you should believe this answer much more).
'a'+'c'='ac'
'p'+'reh'='preh'
'ac' inserted into 'preh' is 'PREACH'.
Can you help me to learn more?
(Other definitions for preach that I've seen before include "Give, eg, a sermon" , "Moralise" , "Speak from the pulpit" , "Pontificate" , "Take a perch to deliver sermon" .)