Quoted By:
Drown
The change in water pressure is high but the problems really start to come about when you go from low to high to low again and since you'd be staying down there you'll just drown. Don't get me wrong, you'll swell up like a balloon but you're not gonna pop or something.
And I'd say the distance down doesn't matter as much as the distance from shore and depending on the traffic in the area.
If you dump somebody 300 miles from the shore you're pretty much guaranteed nobody will find them regardless of the distance down. Even say the body is found like a month later by a fishing ship or something as long as you take the necessary precautions it would be almost impossible to link you to the crime. Just don't leave your DNA on the body.