Electronic Tags are mounted on swimmers to reduce their risk of drowning by identifying when their heads are underwater for periods of time which may indicate a dangerous submersion situation, and for triggering corresponding alerts and alarms. In this method, each monitored person is equipped with a lightweight electronic Tag worn on the body that communicates with monitors that issue the alerts and alarms, including audible and visible distress signals. The monitors, in turn, communicate the alarms to receivers used by supervisory personnel, such as lifeguards or parents. The invention may be used in aquatic environments, such as public recreation facilities, pools, waterfronts, and water parks, as well as in more private settings, such as homes, apartment buildings or hotels.