Officers were called out to McGregor Line and Cemetery Road Saturday afternoon when someone spotted a section of the guard rail down.
Officers determined a vehicle had gone through the rail and into the water.
Chatham-Kent Fire arrived and discovered the car upside down in about 20 feet of water.
The license plate found at the scene was apparently stolen in Waterloo.
The car is now believed to be connected to a vehicle theft in Wallaceburg.
The investigation continues.