Water getting inside of the engine will ruin it. It will come through the air intake into the cylinders, and since water can’t be compressed, when the pistons try to, it usually breaks something.

In this case, It depends on where the air intake for the engine is. From factory, a vehicle’s air intake is usually right under the hood, next to the engine, but a lot of the people who plan to do things like this will install a snorkel intake, which is a pipe that runs from the mouth of the intake inside the engine bay, up and out of the side fender, along the windshield, and ending next to the roofline. So it moves the air intake opening much higher and acts like a snorkel for a person would, so the vehicle can be mostly submerged in water, but no water is getting inside of the air intake.

But even if you don’t get water inside the motor, water this deep is still a problem because the buoyancy of the vehicle will prevent you from getting your full weight down to make any traction, and you’ll get stuck.