Though it might not have saved these individuals, still a valuable skill to have: https://en.wikipedia.org/wiki/Drownproofing

In Drownproofing terminology, the great majority of people are "floaters". That is to say that, with the lungs fully inflated (or say at total lung capacity), they have slightly less specific gravity than water and will not start to sink until they exhale. An average floater has 3–4 lb (1.4–1.8 kg) of positive buoyancy in fresh water. "Sinkers" can also benefit from a modified technique, but will find it more difficult to learn and will probably need specialised coaching.

In the Drownproofing survival technique, the subject floats in a relaxed, near-vertical posture, with the top of the head just above the surface. Using the arms or legs to exert a downward pressure, the subject raises himself sufficiently so that the mouth is above the surface and a breath is taken, before dropping back into the relaxed float. This is done several times a minute (typically between 5 and 10), depending upon the needs of the individual. It is important to keep the lungs fully inflated for the maximum possible time and to exhale and inhale rapidly when a breath is taken. The technique is easy to learn and does not require arduous training or a high standard of physical fitness. With practice, it is possible to remain afloat in this way for a long time with minimal effort. Lanoue taught his students to perform the technique with hands and feet tied, thus demonstrating that it is possible to survive even when injured or otherwise disabled.