On Tuesday, the governor of Louisiana accused FEMA officials of taking too long to recover dead bodies. Last week, the agency asked photojournalists not to take pictures of floating corpses. (The policy was reversed on Saturday.) Most images that have been released show corpses floating on their stomachs. Do bodies always float facedown?
As a general rule, yes. A cadaver in the water starts to sink as soon as the air in its lungs is replaced with water. Once submerged, the body stays underwater until the bacteria in the gut and chest cavity produce enough gas—methane, hydrogen sulfide, and carbon dioxide—to float it to the surface like a balloon. (The buildup of methane, hydrogen sulfide, and other gases can take days or weeks, depending on a number of factors.) At first, not all parts of the body inflate the same amount: The torso, which contains the most bacteria, bloats more than the head and limbs. The most buoyant body parts rise first, leaving the head and limbs to drag behind the chest and abdomen. Since arms, legs, and the head can only drape forward from the body, corpses tend to rotate such that the torso floats facedown, with arms and legs hanging beneath it.
Most dead bodies float this way, but there are exceptions. The smaller the limbs, the more likely a corpse will float facing up—short arms and legs create less drag. Also, if a body stays on the surface of the water for a long time it will release the built-up gas and sink once again. Decomposition continues underwater—more gas accumulates—and the body may become what rescue workers sometimes call a "refloat." Since refloats are at a more advanced state of decay, they may be more evenly bloated and thus more likely to float faceup.
Bodies that are dead before they reach the water could have different floating patterns. A corpse that falls in face-first might remain on the surface, since there would be no way for the air inside the lungs to escape. (A faceup corpse would fill with water and sink in the normal fashion.)
Editorial control over photographs also contributes to a facedown bias. Most photo editors won't publish pictures of a body that could be identified by a friend or family member. Since facedown corpses are likely to be anonymous, they're more suitable for newspapers and television.
Explainer thanks Greg Garneau of the National Press Photographers Association, John Sanders of the National Underwater Rescue-Recovery Institute, Daniel Schultz of the District Six Medical Examiner's Office in Florida, and reader Sara Stewart for asking the question.