Sea turtles cannot breathe underwater, but they have remarkable breath-holding abilities. Typically, a resting or sleeping sea turtle can hold its breath for between 4 to 7 hours by significantly slowing its heart rate to conserve oxygen, sometimes with up to nine minutes passing between heartbeats

. During active periods such as foraging, they usually dive for 20 to 40 minutes before surfacing for air

. In cold water, especially during hibernation or overwintering, some sea turtles can remain submerged for even longer periods, with the longest recorded submersion being about seven hours by a loggerhead turtle in Greece

. However, during routine activity, breath-holding is generally shorter, often between 4 to 7 minutes for species like the Hawaiian green sea turtle

. Freshwater turtles can also hold their breath for extended periods, especially when resting or sleeping underwater, thanks to a slowed metabolism. They can survive several hours submerged under these conditions

. In summary:

• Resting/sleeping sea turtles: 4 to 7 hours underwater
• Foraging/diving sea turtles: 20 to 40 minutes per dive
• Routine active dives (e.g., Hawaiian green sea turtles): 4 to 7 minutes
• Freshwater turtles resting: several hours underwater
• Longest recorded submersion: about 7 hours (loggerhead sea turtle)

These abilities are supported by physiological adaptations such as high oxygen storage in blood and muscles, and the capacity to slow heart rate and metabolism to conserve oxygen

. Thus, how long a turtle can hold its breath depends on species, activity level, and environmental conditions like water temperature.