And I think I would have been really good at this, too.
I was a distance swimmer. Gas tank was not an issue. As we used to say, when the going gets tough, the sprinters get out.
I could not float. Still can't. So I have gotten very comfortable being under water.
My coach was also my lifeguard instructor. He was also the second fastest 200 butterflyer behind Mark Spitz in his day (broke his ribs at the 1972 Oly Trials). During our certification test we had to "save" him. If you did not secure the hold correctly he would attempt to drown you. Even if you did secure the hold correctly he would attempt to drown you, but at least you could survive with the correct hold if you refused to give up.
Did I mention he was a world class butterflyer? His shoulders were as wide as a pool lane. The right hold involved maneuvering behind him, getting his shoulder lodged in your armpit, locking your arms around his body, and pulling him in tight to your chest, while he flailed like a panicked drowning person who was also a recently retired world class swimmer.
He did not drown me.