A city maintenance barge caught the vehicle, which saved the life of the man, police told The Dagger.
Firefighters secured the vehicle, Hurst told Patch.
There were no injuries as a result of the incident, according to Hurst.
Police said the driver was not impaired and would not be charged, The Dagger reported. There was little damage to the barge, police told The Aegis.
A flood watch was in effect for most of Maryland, including Harford County, on Saturday, according to the National Weather Service, which reported drivers should be extra careful on roads due to fog. A small craft advisory was also in effect.