A Corby man who died after going into the River Nene at Whittlesey may have been in the water for up to a week before he was found.
Keith Pettitt (50) was pronounced dead at the scene on Monday after the Skoda Octavia he had been in was recovered from the river.
Police and emergency services were called shortly after 2.30pm to reports that a vehicle had been spotted partially submerged in the water.
It is thought the car may have entered the water as early as November 26.
PC Tim Kirkby, investigating, said: “I would appeal to anyone who saw the vehicle enter the water or saw it being driven along that stretch of road between Tuesday (November 26) and 2.30pm on Monday.”
Yesterday (Tuesday) the road remained closed.
Anyone with any information should call the Roads Policing Unit on 101.