How a painted turtle survives winter under pond ice

Picture a pond in January, sealed under ice. On the bottom, in cold mud, a painted turtle sits and does almost nothing. It may stay that way for months. A 2002 review of the research, by Donald Jackson in the Journal of Physiology, reports that in lab tests that copy winter, painted turtles survived 3 to 4 months at 3 °C (about 37 °F) in water with no oxygen at all.

That is a strange result for an animal that breathes air. The turtle (Chrysemys picta) does not have gills, a secret air tank or a very good book. What it has is a short list of tricks that work together: slow the whole body to a crawl, let the shell soak up the acid that builds up, and take in a little oxygen through other surfaces when the water has some.

This article walks through those tricks, then looks at hatchlings, which spend their first winter in a quite different way. Most of the lab work comes from the western subspecies, so we flag that each time. A result from one subspecies, or from a lab tank, does not automatically describe every turtle in every pond.

Meet the painted turtle

The painted turtle is a mostly aquatic freshwater turtle. The Animal Diversity Web, a University of Michigan database, places it from southern Canada southward and says it lives in quiet, shallow water with a thick mud layer: lakes, ponds, slow rivers, marshes and swamps. Connecticut’s wildlife agency describes a dark shell with olive lines across its plates, black and red marks on the shell edge, and yellow stripes on the head, neck and limbs. Turtles bask on rocks and logs, sometimes stacked on one another, and slide into the water when threatened. A busy basking log looks like a very slow traffic jam.

Painted turtles are also kept in captivity, but this article is not a guide to keeping them or to handling wild ones. Watching from the bank is the safer way to see them.

A pond in winter: where the turtles go

A frozen pond is a closed room. The ice is a lid, and the water below can hold little oxygen. Jackson writes that painted turtles overwinter in ice-covered ponds, sometimes trapped under the ice with no access to the surface, in water or mud with little or no oxygen.

A Government of Canada status report gives more detail on where they sit. Adults hibernate in ponds or streams, usually in shallow water below the depth that freezes, and they stay in one spot or a small area all winter. They rest on muddy bottoms or in muskrat burrows, which is a kind of winter sublet. Connecticut’s agency says turtles there spend winter in mud or decayed plants and come out earlier than other turtles, typically in March.

Hibernating in a group has a cost in some places. The Canadian report says otters can devastate local populations by killing hibernating turtles that overwinter together in exposed areas.

Surviving without oxygen: a slow heart and an antacid shell

Without oxygen, an animal can still make a little energy by breaking down sugar in a way that leaves lactate behind. Lactate is the substance that builds up in tired muscles after a hard sprint. In a turtle that sits for months, it piles up. Jackson reports circulating lactate of 150 millimoles per liter or more after months at 3 °C, and says the animals survive it.

Two things make this possible.

First, the turtle uses almost no energy. One summary of Jackson’s review reports that at 3 °C the metabolic rate of a turtle without oxygen is more than 10,000 times lower than that of a resting mammal of similar size, and that the heart rate averages one beat every 2 to 3 minutes, in extreme cases one beat every 5 to 10 minutes. The review’s abstract, which we did open, confirms the 3 to 4 months and the lactate level, but it does not contain these two figures, and we could not check them anywhere else. Treat them as unconfirmed.

Second, the shell is a chemistry set. Shell and bone make up more than 35% of body mass, according to Jackson. He reports that an estimated 40 to 45% of the body’s lactate ends up there. The acid that comes with lactate is neutralized by carbonate in the shell, which releases calcium, magnesium and carbonate into the blood as buffers. It works a little like an antacid tablet, except the tablet is wearing the turtle.

The Canadian report adds that painted turtles are the most anoxia-tolerant turtles in Canada, and that the western subspecies tolerates long periods without oxygen better than other subspecies. It also says lactate acidosis builds through winter but stays well below the species’ maximum tolerable level, even in the north.

Skin, throat or neither? Breathing when oxygen is there

If the water holds some oxygen, a dormant turtle does not have to go fully without. The Canadian report says that while dormant the animals need much less oxygen and can absorb some from the water through the skin, the lining of the throat and thin-walled sacs near the cloaca (the single body opening used for waste and eggs). It also says they cannot run on oxygen alone through a long winter, so they fall back on the oxygen-free route described above.

Here the sources disagree. Grégory Bulté, an instructor at Carleton University, writes that the “breathing through the cloaca” idea is a popular misconception for North American hidden-necked turtles, which include painted turtles. He says a 2004 test on submerged painted turtles by Jackson and colleagues found no gas exchange in the cloaca and showed that the skin performs this job. Some Australian side-necked turtles do use cloacal sacs for gas exchange, he adds, which may be where the idea got its legs. We lean on the direct test, but the Canadian report’s wording shows the question has not been closed in every source.

Hatchlings: a different winter plan

Hatchlings do not go to the pond. The Canadian report says eggs hatch in fall, but the young stay in the nest chamber, about 10 cm (4 inches) or less below the surface, until spring. Connecticut’s agency says young from late clutches may overwinter in the nest.

Freezing is the problem. The report says a hatchling’s body fluids freeze at about -0.6 °C, and that hatchlings tolerate freezing only if body temperature stays above about -4 °C, so survival often depends on supercooling, which means staying liquid below the freezing point. In the lab they can supercool to about -15 °C. In nature, ice crystals in the nest can set off freezing. The report says sandy, wet soils favor freezing and dry, organic soils favor supercooling.

Snow matters a great deal. In Michigan, the report says, a cold winter without snow, with soil at -7 to -9 °C, killed 45% of hatchlings, while three mild winters with snow-insulated soil above -2 °C killed fewer than 3%. Snow is a blanket, and the turtles are under it.

Sex in this species also depends on nest temperature, with cooler nests giving males and warmer nests giving females, according to Connecticut DEEP. That story has its own article: see the Green sea turtle.

Common myths and mix-ups about turtle winters

Myth: turtles breathe through their butts under ice. For painted turtles, the direct test found skin, not the cloaca, doing the gas exchange.

Mix-up: “hibernating” means a deep sleep. The sources describe a controlled slowdown of the whole body, with chemistry running without oxygen. It is closer to a power-saving mode than to a nap.

Mix-up: everything that survives winter freezes. The Wood frog is famous for surviving winter as ice. Adult painted turtles are described as resting in water below the freezing depth. Hatchlings are the ones that must handle freezing, and they lean on supercooling.

Mix-up: lab numbers describe every pond. The 3 to 4 months at 3 °C come from lab simulations, mostly on the western subspecies. Wild turtles meet ponds that differ in depth, oxygen and temperature.

Mix-up: one winter plan fits all turtles. The Eastern box turtle article describes a land turtle that burrows into soil for winter instead of settling into pond mud, so plans differ between species.

Conservation status

The painted turtle is listed as Least Concern on the IUCN Red List of Threatened Species. That is the category as distributed by GBIF, the Global Biodiversity Information Facility, and we checked it on November 9, 2026. Least Concern means the species was evaluated and does not meet the criteria for a threatened or near-threatened category.

Least Concern does not mean no problems. The Animal Diversity Web calls the species relatively common across most of its range and names loss of freshwater habitat, such as ponds and small lakes, and deaths on roads as threats. Connecticut’s agency says road deaths are significant, often among pregnant females looking for nest sites, that raccoons and skunks raid nests (sometimes 90% or more are lost), and that released pet red-eared sliders compete for food and basking sites. The Canadian report adds that adult survival in some Ontario and Michigan studies was above 0.98 a year, a sign of a long-lived animal. We have no confirmed population trend, because none of our sources states one.

Categories are reviewed and can change, and the copy GBIF distributes can trail the IUCN website by some months, so the date matters. GBIF’s copy does not give the year of the IUCN assessment, so we do not state one. For the current category, check the IUCN Red List itself.