A body sinks in water when its density is greater than the density of the water. This usually happens when the air in the lungs is replaced by water, making the overall density of the body higher than the surrounding water. In living people, lungs filled with air help keep the body buoyant, so it floats or swims. After death, a body initially sinks because the air is expelled or replaced by water, increasing its density. Later, during decomposition, gases produced inside the body cause it to bloat and reduce its density, which can make it float again. Thus, sinking occurs mainly when the body's density exceeds that of water due to air loss or water filling the lungs and tissues.
