What Happens to a Body After Drowning?

A body submerged in water undergoes a distinctive sequence of changes that differs in important ways from decomposition on land. In the minutes surrounding death, the lungs fill with water, the heart may develop fatal rhythm disturbances, and blood chemistry shifts depending on whether the water is fresh or salt. After death, cooler water temperatures and an oxygen-poor environment slow the usual breakdown of tissue, but they also introduce unique processes like adipocere formation and colonization by aquatic organisms. Understanding these changes matters not only for the morbidly curious but for forensic investigators trying to determine how someone died and how long they were in the water.

What Happens in the Final Minutes

Drowning is not one single event but a cascade of reflexes and failures. When a person is suddenly submerged, especially in cold water, two powerful and opposing reflexes can fire at the same time. The cold shock response drives the heart to beat faster through the sympathetic nervous system, while the diving response, triggered by water contacting the face, slows the heart through the parasympathetic system. Researchers have proposed that this simultaneous push-and-pull, called “autonomic conflict,” can trigger dangerous heart arrhythmias and may account for some deaths previously attributed to drowning or hypothermia.¹ In children immersed in cold water (around 11°C), heart rate jumped by about 31% and breathing rate by 58%, peaking within 30 seconds before starting to normalize, though the response was less intense than what is typically seen in adults.²

If the person cannot get their head above water, the sequence continues. The body’s upper airway reflexes initially try to keep water out, which is why people swallow large amounts of water before aspiration begins. Fear, gasping, breath-holding, and vomiting all occur in rapid, overlapping waves.³ Eventually, water enters the lungs, and the consequences depend heavily on the type of water.

Freshwater Versus Saltwater

This distinction matters more than most people realize, because fresh and salt water damage the body through different mechanisms. Freshwater has a lower salt concentration than blood, so when it floods the lungs and gut, it gets absorbed rapidly into the bloodstream. This sudden increase in blood volume can destroy red blood cells, a process called hemolysis, and dilute the blood’s electrolytes. Saltwater, by contrast, has a salt concentration roughly equal to blood, so it does not cause the same rapid absorption or hemolysis. Instead, it draws fluid into the lungs from the surrounding tissue and slightly raises sodium and chloride levels.⁴

Animal studies have shown that the lung damage patterns also differ. In freshwater drowning, the main features are collapsed air sacs and congestion in the lung tissue, with the oxygen exchange capacity dropping initially but starting to recover within a couple of hours. In seawater drowning, the damage is more severe and progressive: massive swelling, heavy immune cell infiltration, and bleeding between the air sacs. The oxygen exchange capacity keeps falling rather than recovering, and far more water remains trapped in the airways.⁵ Pressures in the lung blood vessels spike higher immediately after freshwater drowning but then gradually drop, whereas in seawater drowning those pressures keep climbing.⁵

In practical terms, both types of drowning are lethal because the lungs can no longer exchange gases effectively. But if a near-drowning victim is rescued, the type of water they inhaled can affect the medical team’s approach, since the electrolyte disruptions and the trajectory of lung injury differ.

What Happens Immediately After Death

Once the heart stops, the body begins to sink. Most human bodies are only slightly less dense than water when the lungs are full of air, and once the lungs fill with water and residual air escapes, the body typically sinks to the bottom. How quickly this happens depends on body composition, clothing, and water conditions. A body will generally remain on the bottom until decomposition gases accumulate enough to make it buoyant again.

Meanwhile, the water environment starts altering the body in ways distinct from what happens on land. Skin exposed to water begins to absorb moisture, and the outer layer of the hands and feet wrinkles and eventually loosens. The familiar “pruning” you see after a long bath accelerates after death because the body’s active systems no longer regulate water absorption. Over days, the skin of the hands can become so waterlogged that it peels off in a glove-like sheet, which forensic examiners sometimes use to attempt fingerprint recovery.

Decomposition in Water Versus on Land

Decomposition underwater proceeds more slowly than on land, primarily because the water is usually cooler than the surrounding air and because the submerged environment is low in oxygen. These conditions limit the activity of the bacteria and insects that drive rapid breakdown on land.⁶ However, once a body is pulled from the water, the process accelerates dramatically. The tissues are already saturated with moisture, and exposure to air and warmth gives decomposition bacteria the oxygen boost they need to work much faster than they would on a body that had been on land the entire time.

The rate of underwater decomposition is not uniform. Season matters enormously: bacterial diversity on submerged remains varies substantially between early winter and late winter, and water chemistry factors like pH, salinity, and dissolved oxygen all drive shifts in the microbial communities doing the actual work of breakdown.⁷ Even what a person is wearing makes a difference: one study found that synthetic nylon clothing led to different bacterial communities colonizing the remains compared to cotton or bare skin.⁷

As decomposition progresses, internal bacteria, especially from the gut, produce gases like methane and hydrogen sulfide. These gases inflate the abdomen, face, and other soft tissues, eventually making the body buoyant enough to float back to the surface. In warm water this can happen within days; in very cold water it can take weeks or even months. The bloated, discolored appearance of a body recovered from water is largely the result of this gas production combined with waterlogging of the tissues.

Adipocere and Long-Term Preservation

One of the most distinctive things that can happen to a body in water is the formation of adipocere, sometimes called “grave wax.” This waxy, soap-like substance forms when body fat undergoes an incomplete chemical transformation driven by bacteria in a wet, oxygen-poor environment.⁶ The fat’s unsaturated fatty acids, like oleic acid, are converted into saturated ones, primarily palmitic acid.⁸

Adipocere can begin to appear surprisingly quickly. In one study of bodies recovered from a single shipwreck in cold sea water (around 10 to 12°C), initial patches of adipocere were detected on the skin’s underlying fat layer as early as 38 days after immersion.⁹ The bacterium most implicated in the process, Clostridium perfringens, thrives in temperatures between roughly 21°C and 45°C, so warmer water can speed things up, but the process occurs across a range of conditions as long as moisture and low oxygen are present.⁸

What makes adipocere forensically valuable is that it can preserve the body’s external shape, and sometimes even wound patterns, for months or years. Bodies recovered from water with extensive adipocere formation can still yield useful information about identity and manner of death long after soft tissue would otherwise have been lost.

Aquatic Scavenging

Bodies in water are subject to feeding by aquatic animals, and the range of creatures involved is broader than most people assume. In marine environments, large predators can leave dramatic evidence. One forensic investigation of a body recovered from the Indian Ocean documented a large, semicircular wound about 42 centimeters across, with distinct bite marks on the torso strongly suggesting a shark attack.¹⁰ But much of the scavenging seen on bodies in water comes from smaller creatures. Fish, crabs, and crayfish nibble at soft tissues, particularly around the face, hands, and ears.

In one Australian case, investigators found small irregular patches of missing skin, some linear and parallel, that initially resembled suspicious injuries. The marks turned out to have been caused by freshwater yabbies, a type of crayfish. The damage was concentrated on the ear lobes, a pattern the investigators had not previously documented.¹¹ Cases like this are a reminder that post-mortem animal feeding can easily be confused with ante-mortem injuries, a potentially serious problem in death investigations.

How Forensic Examiners Determine Drowning

Proving that someone actually drowned, rather than dying from something else and then ending up in water, is one of the harder problems in forensic medicine. There is no single test that definitively confirms drowning. Instead, investigators rely on a combination of evidence from autopsy, imaging, chemistry, and microscopy.

Post-mortem CT scanning has proven useful because it can detect some hallmarks of drowning that are difficult to see at a traditional autopsy. In drowning cases, fluid is consistently present in the airways. Water distends the stomach and duodenum from swallowing, and the paranasal sinuses fill completely. CT scanning can also directly visualize bronchospasm and blood dilution, findings that are hard or impossible to confirm during a conventional autopsy.¹²

Another approach involves diatoms, the microscopic algae found in virtually every natural body of water. When a living person inhales water, diatoms enter the lungs and can be carried by the bloodstream to distant organs like the liver, kidneys, and bone marrow. Finding diatoms in these closed organs provides evidence that water was actively inhaled while the heart was still beating, as opposed to water passively seeping in after death.¹³ The test is not perfect, since contamination can occur, but it remains one of the most widely used supplemental tools in drowning investigations.

Chemistry of the Eyes

One of the more intriguing forensic techniques involves the fluid inside the eyes. Vitreous humor, the gel that fills the eyeball, is relatively insulated from post-mortem contamination and bacterial activity, making it a more stable sample than blood for chemical analysis after death. In saltwater drowning, the sodium and chloride levels in the vitreous become significantly elevated compared to people who died in saltwater from other causes and were simply immersed after death. Researchers have proposed that a combined sodium-and-chloride level of 284 mmol/L or higher in the vitreous is consistent with saltwater drowning, while a level below 258 mmol/L argues against it.¹⁴ Values in between are inconclusive and require additional evidence.

Magnesium levels in the vitreous add another layer of information. When immersion time is short, under about an hour, vitreous magnesium does not rise significantly in saltwater drowning cases compared to deaths unrelated to water. But with longer immersion times, magnesium climbs significantly.¹⁵ This distinction is useful because it helps investigators separate the chemical changes caused by the drowning itself from changes caused simply by soaking in saltwater after death.

Estimating How Long a Body Has Been in the Water

Pinpointing the post-mortem submersion interval, or how long a body spent in the water before recovery, is critical for death investigations but notoriously difficult. On land, forensic entomologists can study fly larvae to estimate time of death with reasonable precision. Underwater, those familiar insect clocks are mostly absent, and investigators have to rely on less developed methods.

One approach uses a scoring system based on visible decomposition changes. A method developed for bodies recovered from the North Sea assigns scores to specific signs of decay, and those scores correlate strongly with the amount of time spent submerged. The system showed high agreement between different examiners, suggesting it is reproducible and valid as a practical tool.¹⁶

Microbial communities offer another promising avenue. As a body decomposes underwater, the types of bacteria living on and around it change in a somewhat predictable sequence. In a study of submerged carcasses in a tidal river, the three most abundant bacterial families shifted across decomposition stages, and models built from these microbial patterns could predict the accumulated time-temperature exposure with an error of roughly plus or minus 2.7 days at the study’s average water temperature.¹⁷ Aquatic invertebrates colonizing the body, including certain species of insects, crustaceans, and snails, are also being studied as potential biological clocks for submersion time.¹⁸ These methods are still being refined, but each adds a piece to a puzzle that no single technique can solve alone.

Why Toxicology Gets Complicated in Water

If investigators need to know whether drugs or alcohol played a role in a drowning, water immersion creates serious headaches. Blood samples from a body recovered from water are often diluted (in freshwater cases) or contaminated with salts (in saltwater cases), and decomposition bacteria can both produce and destroy alcohol and other substances. Compared to the relatively well-studied problem of post-mortem alcohol changes, very little is known about what happens to the concentrations of other drugs in a body that has been submerged for an extended period. This gap in knowledge means that toxicology results from drowning cases often come with wide margins of uncertainty, and a negative drug screen does not necessarily mean the person was sober at the time of death. For investigators, the practical takeaway is that toxicology in water-recovery cases demands extra caution in interpretation, and a finding that would be straightforward in a body found on land can become ambiguous once water has been part of the equation.

Freshwater Invertebrates as Forensic Tools

On land, the arrival and development of blowfly larvae is one of the most established methods for estimating time since death. Underwater, a parallel system is being developed using aquatic invertebrates. Freshwater bodies attract a succession of organisms, from algae and bacteria to insect larvae, leeches, snails, and crustaceans, and the mix of species present on a body changes over time in a way that can be mapped to submersion duration. Researchers have developed sampling protocols specifically designed for recovering these organisms from bodies found in both flowing and still water, aiming to standardize the process so it can be applied reliably in casework.¹⁹ The field is still young compared to terrestrial forensic entomology, but the concept is sound: just as the species of insects on a body on land tell a story about time, the community of aquatic organisms on a submerged body tells its own story. The challenge lies in the enormous variability of aquatic ecosystems, where factors like water temperature, flow rate, season, and local species diversity all influence which organisms show up and when.