This is a very good starting reference point even though its a blog.
http://killingkillers.blogspot.com/p/drowning-forensics.html?m=1
"If a victim is not promptly retrieved at death, then, without exception and no matter how deep or how swift the water may be, their corpse will continue to drift downward until it reaches the bottom. This is where it will remain in a somewhat fetal position until gases from putrefaction cause it to rise to the surface once more. A semi-fetal posture is the norm for all drown victims, so if divers do locate such a body before it ascends, but it isnt in this pose and/or the head is seen to be tilted to one side, they will include these observations in their police recovery report, as it reveals the victim died on land and was put in the water post-rigormortis.
Typically, once the body does emerge on its own, it will surface in the general vicinity of where the victim originally went under. From this location the water may then carry the corpse along for quite a distance, depending on the strength of the currents or if it becomes ensnared and is thereby prevented.
Refloat largely varies on the waters depth and temperature, taking only a matter of hours to occur if extremely warm and up to two weeks or longer if at 40 degrees Fahrenheit or less. The timetable, therefore, is not fixed but is loosely as follows: at 40 degrees Fahrenheit it takes approximately fourteen to twenty days for a drown victims corpse to resurface; at 50 degrees ten to fourteen days; at 60 degrees seven to ten days; at 70 degrees three to seven days; and at 80+ degrees one to two days or sooner. In very cold and very deep bodies of water, like certain oceans or the Great Lakes of North America, its not unusual at all for a drown victim to never resurface, lying on the bottom in a state of suspended decomposition until their body eventually disintegrates or is otherwise destroyed.
But in temperate oceans, rivers, lakes, ponds, pools, reservoirs, quarries, or the like, a corpse will inevitably rise again sooner or later, occasionally exploding to the surface if it was deliberately anchored. And when it does reappear, if the person did genuinely die from drowning, then they will always be discovered floating face down in the water, with the head drooping forward and lower than the rest of the body. Lividity, the pooling of blood and fluids, will then have permanently settled into the under regions of the corpse by then, weighting it from beneath and essentially acting as a ballast so that, even when disturbed, say by a collision with a boat, it will return to this original position."
More at link above.
