Const. Brian Montague says the 81-year-old man was heading downtown on Monday night when he lost his way in Vanier Park.
Montague says due to darkness and bad weather, the man ended up driving down the ramp and into the water.
By the time police arrived, the car had sunk and only its back end was visible.
Montague says five officers swam to the car and smashed the rear window, allowing the dog to swim free and pull out the driver.
Both the driver and his pet are recovering.