Having turned left, travelled by the river (7)
I believe the answer is:
derwent
'the river' is the definition.
(I've seen this before)
'having turned left travelled' is the wordplay.
'having turned' says the letters should be written in reverse.
'left' becomes 'red' (I've seen this in other clues).
'travelled' becomes 'went' (I've seen this before).
'red' written backwards gives 'der'.
'der'+'went'='DERWENT'
'by' acts as a link.
(Other definitions for derwent that I've seen before include "River in England and Australia" , "River; lake, --water" , "Name of several rivers" , "N. Yorkshire river" , "English river" .)