Treading water or water treading is what a swimmer can do while in a vertical position to keep their head above the surface of the water,merely staying in one place
Water treading technique is used by lifeguards and other aquatic rescue professionals because of its efficiency and simplicity. It does not occupy the hands as these professionals often have to perform first aid as they are swimming to safety.
Water polo players & synchronized swimmers use water treading techniques for stability and height above the water while leaving the hands free to perform movement or action.
Water treading technique is practiced by soldiers as one of their water survival routine
For swimmers, treading water is ideal in situations where you need to look at your surroundings