With proper bags you can lift a car off of the bottom in 5 feet of water. I had one a few years ago that was swept down a bayou. I had to lift and float it to an extraction point 300 yards upstream in 5' of water. You have to "cradle" the vehicle with straps, or solid attachment points, which hold the bags low and raises the vehicle off of the bottom. It is not as easy as it sounds, due to stretching straps and such, but it is not terribly difficult either. Generally a strap to the vehicle and cable from a tow truck works fine, unless there are obstructions between the object and the bank. Cranes are great, but not feasible for recovering vehicles as they are cost prohibitive. With proper bags or a tow truck it can be done safely, but not without the proper training as there are a lot of dynamics involved. My facebook page has quite a few photo's of jobs, from vehicles to airboats, etc. The big thing is to be careful and don't take on something that you are not positive you can do safely. You need the right equipment for the job.
Mark Michaud | Facebook