This is kinda interesting
Fluid Dynamics -
Water weighs about 62.4 pounds per cubic foot and typically flows downstream at 6 to 12 miles an hour. When a vehicle stalls in water, the water’s momentum is transferred to the car. For each foot the water rises, 500 pounds of lateral force are applied to the car. For each foot the water rises up the side of the car, the car displaces 1,500 pounds less for each foot the water rises. Therefore, most cars will float in just two feet of water.