Can Turtles Breathe Underwater and How They Do It?

Many turtles can extract oxygen directly from water without surfacing, though the method varies wildly depending on the species. Some freshwater turtles pull water in through their rear end and absorb oxygen through specialized tissue, a process researchers have sometimes called “cloacal respiration” and popular science has dubbed “butt breathing.” Others absorb oxygen through their skin or the lining of their throat. Marine turtles, by contrast, rely almost entirely on their lungs but have evolved dramatic physiological tricks to stretch a single breath across hours of deep diving. The full picture is stranger and more varied than most people expect.

Cloacal Respiration in Freshwater Turtles

The most eye-catching form of underwater gas exchange in turtles happens through the cloaca, the single opening at the base of the tail that serves as the exit for the digestive, urinary, and reproductive systems. Several Australian freshwater turtles have evolved pouches called cloacal bursae that branch off from this opening. These bursae are lined with thin, highly folded tissue packed with blood vessels, and the turtle rhythmically pumps water in and out across them to extract dissolved oxygen.

The white-throated snapping turtle (Elseya albagula) is one of the most studied examples. In laboratory measurements, aquatic oxygen uptake accounted for roughly 70% of its total oxygen needs, and the cloacal bursae alone were responsible for about half of all underwater oxygen absorption.¹ That is a remarkable number. It means the turtle can spend the vast majority of its time submerged, surfacing only briefly and infrequently.

Another well-studied species, the Fitzroy River turtle (Rheodytes leukops), adjusts its cloacal pumping rate depending on how much oxygen is dissolved in the surrounding water. When oxygen levels are normal, it relies heavily on cloacal respiration. When oxygen drops, it shifts strategy, slowing cloacal ventilation and conserving its existing oxygen stores to extend its dive time rather than trying to extract what little gas remains in the water.² This kind of active regulation shows that cloacal respiration is not a passive accident but a finely tuned system responsive to environmental conditions.

What Makes the Cloacal Bursae So Effective

The internal anatomy of these bursae explains why they work as gas exchangers. Histological studies of several Australian freshwater turtle species (family Chelidae) reveal that the cloacal bursae are lined with dense, fingerlike projections called villi, along with deeply folded mucosal tissue. These structures massively increase the surface area of the epithelium exposed to water, much the way the lining of a mammalian intestine increases its absorptive area. Electron microscopy of this tissue shows structural features consistent with active exchange functions, including thin barriers between the water and the underlying blood supply.³

The bursae do more than just exchange gases. The same study found that these tissues also absorb calcium from the surrounding water, suggesting the bursae serve as a multipurpose interface between the turtle’s body and its aquatic environment. Dissolved minerals and oxygen flow in, waste products flow out. Not every freshwater turtle has bursae this well developed, though. The degree of cloacal specialization varies across species, and turtles that spend less time submerged tend to have less elaborate bursal tissue.

Skin and Throat Breathing

Cloacal respiration is the most dramatic form of underwater gas exchange, but it is not the only one. Many aquatic turtles also absorb some oxygen directly through their skin, a process called cutaneous respiration. Any thin, well-vascularized skin surface in contact with oxygenated water will passively exchange some gas, and turtles that spend long periods submerged tend to have thinner skin in key areas, particularly around the throat, the limb folds, and the cloacal region.

Soft-shelled turtles take this to another level. Their shells are covered with leathery skin rather than hard, keratinous scutes, which gives them a larger surface of permeable tissue. Some soft-shelled species also exchange gases and excrete waste through the lining of the throat and mouth, a process called buccopharyngeal respiration. The Chinese soft-shelled turtle (Pelodiscus sinensis), for example, is known to use its buccopharyngeal epithelium as a major route for excreting urea. During periods when the turtle is out of water, urea excretion drops by as much as 82 to 99% because the throat lining can no longer be flushed with water.⁴ The throat lining in these turtles is not just a minor supplement; it is a primary exchange surface that the animal depends on.

Together, these non-lung pathways mean that many freshwater turtles can stay submerged for surprisingly long stretches. But none of these mechanisms produce as much oxygen as lungs do for an active, warm animal. Turtles that rely on aquatic respiration generally have low metabolic rates and are sitting still on the bottom, not swimming vigorously. Activity demands lungs.

How Painted Turtles Survive an Entire Winter Without Oxygen

North American painted turtles (Chrysemys picta) overwinter at the bottom of frozen ponds and lakes, buried in mud beneath a cap of ice that can persist for months. In many of these ponds, dissolved oxygen is consumed by decomposing organic matter long before the ice melts, leaving the water effectively anoxic. The turtles survive for three to four months at around 3°C with no oxygen at all. This is not underwater breathing. It is the opposite: surviving prolonged oxygen deprivation by shutting down almost everything that requires it.⁵

The trick involves two coordinated adaptations. First, the turtle dramatically depresses its metabolism. Both the pathways that produce cellular energy and the processes that consume it, such as ion pumping across cell membranes, slow to a fraction of their normal rate. This reduces the rate at which the turtle burns through its stored fuel and slows the buildup of lactic acid, the toxic byproduct of anaerobic metabolism. Second, the turtle exploits its own skeleton and shell as a chemical buffer to neutralize the lactic acid that does accumulate. By the end of a long winter, circulating lactate levels in these turtles can exceed 150 millimoles per liter, a concentration that would be lethal in almost any other vertebrate.⁵

The Shell as a Chemical Shield

The shell’s role in surviving anoxia deserves its own discussion, because it is genuinely one of the more surprising adaptations in vertebrate biology. As lactic acid builds up in the blood, the shell releases calcium and magnesium carbonates into circulation. These carbonate ions act as chemical buffers, neutralizing acidity the way an antacid tablet works in your stomach. At the same time, the shell actively absorbs lactate from the blood and stores it within its own tissue.⁶

Measurements of painted turtles held without oxygen at 3°C showed that roughly 44% of the total lactic acid in the body ended up sequestered inside the shell. The lactate concentration within the shell’s water compartment reached staggering levels. Combined with the release of shell carbonates, the shell may account for up to two-thirds of all lactic acid buffering in the animal.⁷ The shell is not just armor. It is a metabolic organ that keeps the turtle’s blood chemistry survivable when oxygen is unavailable.

Not all turtle shells buffer equally well. Softshell turtles (genus Apalone), whose shells are less mineralized, release only about a quarter as much buffer per gram as painted turtles do. Their blood calcium and magnesium also rise less during anoxia. Although softshell turtle shells still absorb lactate at a comparable rate, the weaker buffering response correlates with poorer anoxia tolerance overall.⁸ This makes intuitive sense: if your shell is your main chemical defense against acid buildup, a less mineralized shell means a weaker defense.

Recent work on young painted turtles has added a wrinkle. Hatchlings and juveniles lost their ability to respond to stimuli after about 39 to 42 days of anoxia, with no significant difference between the two age groups. However, the limiting factor for younger turtles appears to be stored glycogen, the fuel that drives anaerobic metabolism, rather than buffering capacity.⁹ In other words, young turtles run out of fuel before they run out of buffer. Adults, with larger glycogen stores, can push past that limit, and the shell’s buffering becomes the more critical factor.

How Marine Turtles Manage Long Dives

Sea turtles are a different story. They do not have cloacal bursae or heavily vascularized throat linings adapted for aquatic gas exchange. They are lung breathers, full stop. But they are astonishingly good at making a single breath last. A resting green sea turtle can stay submerged for several hours during sleep, and loggerheads routinely make deep foraging dives.

The primary mechanism is cardiovascular: sea turtles slow their heart rate dramatically when they dive. In free-ranging loggerhead sea turtles fitted with biologging devices, heart rate during dives averaged about 13 beats per minute, compared with about 21 beats per minute at the surface, a reduction of roughly 39%. The degree of slowing varied between individuals, ranging from 23% to 61%. At the deepest dives, exceeding 140 meters, heart rate temporarily dropped to around 2 beats per minute despite the turtle actively swimming with its flippers.¹⁰

Slowing the heart reduces the rate at which oxygen is delivered to and consumed by the tissues, effectively rationing a finite air supply. The deeper the dive, the greater the heart rate reduction, which suggests the turtles are actively regulating this process rather than passively slowing down. It is the same principle behind the mammalian dive reflex seen in seals and whales, though the specific physiology differs.

Buoyancy management is the other piece of the puzzle. Marine turtles appear to use their lungs not only as oxygen stores but also as buoyancy regulators. By adjusting lung volume before or during a dive, a turtle can control how much effort it needs to stay at a given depth. Less effort means less oxygen burned.¹¹ Among air-breathing divers, this dual use of the lung may be most highly developed in marine turtles.

How Hatchling Sea Turtles Start Out

You might expect baby sea turtles to need a transition period before their respiratory system catches up to adult performance, but that does not appear to be the case. Studies of hatchling leatherback and other sea turtle species found that by the time they emerge from the nest, their resting breathing pattern already resembles that of a diving adult: a single breath followed by a long pause, a slow breathing rate, and a high metabolic rate.¹² Their respiratory pattern did not change significantly over the first several days after hatching. This makes practical sense. Sea turtle hatchlings enter the ocean within hours of emerging and immediately begin a sustained swimming frenzy that lasts days. They need a functional dive-capable respiratory system from the moment they hit the water.

Why Water Quality Matters for Turtle Breathing

For species that depend on dissolved oxygen in the water, the quality and oxygen content of their habitat directly affects their ability to stay submerged. The Fitzroy River turtle’s behavioral shift during low-oxygen conditions illustrates this: when dissolved oxygen drops, the turtle cannot simply pump faster and get what it needs. It has to switch strategies entirely, conserving oxygen and shortening its effective underwater endurance.²

This has real conservation implications. Nutrient pollution from agricultural runoff feeds algal blooms, and when those blooms die and decompose, they consume dissolved oxygen, creating hypoxic zones. Dams and water impoundments alter flow regimes, replacing fast-flowing, oxygen-rich riffle habitats with still, warm reservoirs where oxygen levels are lower. For turtles like R. leukops and E. albagula, which evolved in well-oxygenated rivers, these changes can undermine the very mechanism they depend on to stay submerged and avoid predators. A turtle that has to surface more often because the water is oxygen-poor is a turtle that is more exposed to threats.

Temperature compounds the problem. Warmer water holds less dissolved oxygen, and a warmer turtle has a higher metabolic rate demanding more of it. Climate projections that push freshwater temperatures upward in Australian river systems could squeeze cloacal-breathing turtles from both directions at once. Conservation biologists working on these species increasingly view water oxygenation as a habitat variable just as critical as food availability or nesting substrate.

The Spectrum of Underwater Survival Strategies

It is worth stepping back and recognizing how broad the range is. At one end sit marine turtles, which are committed lung breathers that manage their oxygen budgets through cardiovascular control and buoyancy regulation. In the middle are semi-aquatic pond turtles that absorb modest amounts of oxygen through their skin and throat but still surface regularly. At the far end are the cloacal-breathing Australian river turtles, which get the majority of their oxygen from the water and rarely need to surface at all under normal conditions. And then there is the painted turtle’s overwintering strategy, which sidesteps the question of breathing entirely by shutting metabolism down to a point where oxygen is not needed for months.

These strategies are not mutually exclusive within a species. A painted turtle uses its lungs in summer, may absorb some oxygen through its skin and cloaca while resting on the bottom of a pond, and then switches to full anaerobic survival during a frozen winter. The Chinese soft-shelled turtle uses lungs on land but its throat lining becomes the dominant route for waste excretion when submerged. The strategy an individual turtle employs at any given moment depends on temperature, activity level, oxygen availability, and season. Turtle respiration is less a fixed trait and more a flexible toolkit shaped by millions of years of adapting to life at the boundary between water and air.