A 55-year-old man and his dog were found dead on a canal boat in Banbury on Thursday.
It is thought the well-known boater and his pet died in an accident.
The ambulance service was first on the scene at the Oxford Canal, Tramway Road, at around 1.30pm, but called the fire and rescue service for assistance.
A fire engine from Banbury was sent and firefighters wearing breathing apparatus and carrying gas monitoring equipment went on board the boat.
No toxic gases were discovered and the boat was declared safe, but the man and his pet dog were declared dead at the scene.
The death is being treated as unexplained and Thames Valley Police are investigating.