Over there in dinghy on Derwent (6)
I believe the answer is:
yonder
'over there' is the definition.
(archaic preposition meaning 'over there')
'in dinghy on derwent' is the wordplay.
'in' indicates a hidden word.
'YONDER' is hidden within 'dinghy on derwent'.
(Other definitions for yonder that I've seen before include "At a distance but in sight" , "See Rodney over there" , "Distant but within sight" , "In that direction" , "Rodney (anag.)" .)