Speak to a very quiet swimmer (8)
I believe the answer is:
approach
'speak to' is the definition.
(I've seen this before)
'a very quiet swimmer' is the wordplay.
'very quiet' becomes 'pp'.
'swimmer' becomes 'roach' (roach is a kind of fish).
'a'+'pp'+'roach'='APPROACH'
(Other definitions for approach that I've seen before include "technique" , "Come closer" , "golf shot" , "Come near - means of access" , "Move towards" .)