Interesting.  Did you know that buoyancy can depend on body fat and saltiness of the water?  Higher leves of both can make a person more buoyant.
When you swim, he buoyancy  can depend on how much body fat and how salty the water is
I love to swim and it keeps me in shape Nice!  It's a good "low-impact" sport, compared to running. Yes and I have lung disease its very easy for me to exercise in water, much easier than a gym workout Oh I see!  And swimming is also useful for survival, right? Yes and its also low impact on my bones and joints. Older people really benefit from swimming It's low-impact because the human body is only slightly less dense than water, which allows the water to support a person's weight Oh ok that makes a lot of sense and I noticed I do not get as short of breath swimming versus gym workouts
Higher levels of body fat and saltier water both lower the relative density of the body and increase its buoyancy.