As an aquatic scientist for years and being into photography I drowned five cameras. I only drowned one Nikon as I had taken precautions against such events. I have had them ruined on a quick dunk, and the Nikon (D70) was retrieved after 33 days underwater. Some of these accidents happened when I was nearly broke in grad school. Today they would be equally deadly as I am retired with less to spend.
All of these cameras were totaled. I kept a few as reminders. Especially the D70. I use a TamRac Velocity 6X or 7X bag in the field with a couple of ziplock bags. These work quite well for a dunk even if I am wading all day.. I take out the camera when I am about to shoot and sometimes I can get ready to shoot pretty quickly. The only cameras I use for underwater photos have housings and all cost more than the camera
AdamZ's advice on salvage for parts may work well. I can say with considerable sadness a quick dunk is usually fatal. The D70 Image Capture card was fully intact and had some images on it I really treasure. Prevention I believe is the primary route here, and all measures after the fact (dunking the camera) are only feeble attempts. I use a Pelican waterproof case for our D7000s just to carry them in. In fact we own several pelican cases for various movie cameras, some we use with UW housings but the bare cameras are usually transported in these waterproof cases. But I find them OK for a boat. Wading in chest high waders, I switch to the TamRac velocity cases and the ziplock plastic bags. But once the camera is out of the case (say on a jet boat where our "best" D7000 and higher end lens is tonight) it is at risk. Rain...... a Nikon will tolerate quite well. Spray from a boat, is asking for trouble, but taking it for a "swim" is pretty much the end of that camera as you knew it. Even a repair will actually cost more than it is worth.