This writer, inspired by that virtually small river (6)
I believe the answer is:
thames
'river' is the definition.
(English river)
'this writer inspired by that virtually small' is the wordplay.
'this writer' becomes 'me' (the person who wrote the clues).
'inspired by' indicates putting letters inside (some letters breathed in or 'inspired' by others).
'virtually' means to remove the last letter (all but the last letter).
'small' becomes 's' (abbreviation - e.g. clothes size).
'that' with its last letter removed is 'tha'.
'tha'+'s'='thas'
'me' placed inside 'thas' is 'THAMES'.
(Other definitions for thames that I've seen before include "Sam the river" , "Shipping forecast area" , "'Old Father ___'" , "London flood control" , "The Ma's in the river" .)