Abstract: A system is disclosed for locating swimmers who could be in danger of drowning, as determined by preset parameters such as the time duration that they remain at a depth where breathing is impossible. In this system, each individual swimmer wears a SONAR Swimmer Location Monitor (SSLM). This is a miniature electronic device that not only determines the extent of the swimmer's danger but also emits an ultrasonic alarm signal whenever such danger exists. At each occurrence, an alarm, which may be audible and/or visual, is sounded on the surface. Meanwhile the swimmer's location is tracked in real time from the signals received on a hydrophone array deployed along the perimeter of the swimming area. These signals are combined in a central processor and the computed real-time location is displayed graphically on a monitor to guide the guard personnel in rescue operations. The invention is intended for use in pools, beaches, water parks, and other swimming areas.