But even treading water for that long is no mean feat for a 57 years old
The US Navy taught all students what they called "drown proofing". You float in a fetal position, just the back of the head and nape of neck will be above water, when a breath is needed you raise the head and make a sweeping motion with your hands, once the breath is taken you collapse again into the fetal position. Takes absolutely no energy, survival time would be dictated by the environment - water temp etc. They made students run a cross country where the finish line was in the pool where you had to stay for 30 minutes, the exercise was to show that even in an exhausted state the drown proofing method was no issue.