Police were called as a car crashed into a ditch in Deeping and a car went into the water, with a man in his 70s inside.
A spokesman from Lincolnshire Police said: "At 10.52am we responded to a report of a vehicle in a ditch in Main Road, Deeping St Nicholas. The ditch contained water and there were no other vehicles directly involved.
"A man in his 70s was in the vehicle and sadly did not survive. This is not being treated as suspicious and this will be now be referred to the coroner."